The word genocide has become popular again and is spread throughout news reports, most recently concerning the charges brought against General Augusto Pinochet, the former Chilean dictator. At other times the word is used to describe crimes carried out in the former Yugoslavia.

Generally, it refers to criminal acts committed against politically-defined groups or to expulsion on a mass scale or "ethnic cleansing".

The overuse of the word has led to desensitisation about what genocide really means. There exists a dangerous illusion that crimes against humanity and the crime of genocide are essentially the same.

We have lost the meaning of the word genocide, and yet no more heinous crime exists. Nothing is graver in a criminal sense than a deliberate state policy to exterminate a people based on their ethnic identity. Under international law, the crime of genocide is considered the most serious crime against humanity. Genocide is at the apex of international humanitarian law.

It is the ultimate crime.

Fifty years ago next Wednesday, on December 9th, 1948, the Convention on the Prevention and Punishment of the Crime of Genocide was adopted unanimously by the United Nations General Assembly. It was a milestone event - the creation of the world's first human rights treaty, the first truly universal, comprehensive and codified protection of human rights.

The genocide convention preceded the Universal Declaration of Human Rights by 24 hours. And while the Universal Declaration was an affirmation of human rights, the genocide convention was a legally binding treaty.

Those states which later went on to ratify the genocide convention are legally obliged to act whenever genocide is suspected. Ireland ratified the genocide convention on June 22nd, 1976.

Once genocide is suspected, state signatories have the legal obligation to intervene to stop it. Within the genocide convention is enshrined the promise "never again". A direct result of the Holocaust and the revulsion at the policy to systematically exterminate the Jews, the genocide convention was of unique and symbolic importance.

The genocide convention stood for a fundamental and important principle; that whatever evil may befall any group, nation or people, it was a matter of concern not just for that group, but for the entire human family. Like the fact of the Nazi Holocaust, the very idea of genocide beggars belief.

Genocide extends beyond killing for it covers the prevention of birth: in order to annihilate a people, it is necessary to kill women and children.

Genocide is a deliberate attempt to reconstruct the world. Genocide is a premeditated crime with clearly defined goals. It does not break out spontaneously. It is incited, it is planned and organised.

A key element in the crime of genocide is a racist ideology which is used to legitimise any act, no matter how horrendous.

In the Holocaust, Nazism used a racist ideology which identified the German people as possessing a distinct identity based on blood. Jews, Gypsies and homosexuals were not defined as volk but inferior and alien beings who might pollute the people.

Genocide progresses by stages. Genocide needs participation of the citizenry. Propaganda is used to spread the ideology and define the victim as being outside human existence: vermin and subhuman. People are deemed not fit even to serve in a slave capacity.

With genocide, a racial theory is transformed into practice and the more extreme the racism the more likely is genocide. Genocide is difficult to comprehend by those living elsewhere because it is seen as an aberration rather than a system.

The word was coined by a Polish lawyer, Raphael Lemkin, a scholar and Professor of Family Law in Warsaw. It was a hybrid word consisting of the Greek prefix genos, nation or tribe and the Latin suffix cide, killing.

When Nazi Germany invaded Poland in 1939, Lemkin resisted and was wounded. He hid in forests for six months before eventually escaping to Sweden. Only Lemkin and his brother survived in a family of some 70 members.

In Sweden, he began to collect copies of laws and decrees of the puppet regimes in the countries of occupied Europe, the factual evidence of the German techniques of occupation.

Lemkin realised that in enforcing their new order, the Germans had prepared and waged a war not merely against states and armies, but against peoples. He said his documentary proof would convince those doubters who found it hard to believe that the Axis regime was as cruel and as ruthless as described.

DURING the summer of 1942 Lemkin lectured at the US War Department and he began to write a book, published in 1944, which contained the word genocide for the first time.

The preface explains: "The practice of extermination of nations and ethnic groups as carried out by the invaders is called by the author `genocide'."

In Chapter Nine, Lemkin defines genocide: "It is intended . . . to signify a co-ordinated plan of different actions aiming at the destruction of essential foundations of the life of national groups, with the aim of annihilating the groups themselves."

The book, Axis Rule in Occupied Europe, was published by the Carnegie Endowment for International Peace in Washington DC, and this definition of genocide was the first detailed effort to describe the true nature of what was happening at the time in occupied Europe.

The book explains that the intention of the Nazi regime was to weaken the subjugated people for decades. The plan of genocide was adapted to political considerations in different countries.

A distinction was made between those related by blood to Germans - the Dutch, the Norwegians - and those not related, the Poles and the Slovenes.

The first group could be Germanised. In Poland, it was Hitler's view, only the soil in Poland "could profitably be Germanised". Some groups - such as the Jews - were to be destroyed completely.

Lemkin wrote that the technique of mass killing was employed mainly against Poles, Russians and Jews and he quoted a report from 1943 which described how Jews were being transported to Poland, "the principal Nazi slaughterhouse".

Lemkin believed the techniques of the Nazi genocide were so terrible that there must be an immediate change in international law. Genocide had to be dealt with by the whole international community.

Its prohibition was particularly important in Europe where "certain national groups may be obliged to live as minorities within the boundaries of other states". If these groups were not adequately protected, such lack of protection would result in the disorganised emigration of the persecuted.

This was an international problem which demanded an international solution; without the protection of international law no people on earth could be sure of continued existence.

Lemkin was legal adviser to the US Chief Prosecutor at Nuremburg and at international legal meetings he began to outline ideas for a change in international law.

For the next two years, he pleaded and pressed for an international genocide convention. He had hoped to have genocide recognised at the Paris peace conference in 1945 but was unsuccessful.

He turned to the United Nations and, waging a one-man campaign in a dozen languages, he lobbied the delegates. He represented no government and no organisation. A familiar figure in the early years at UN headquarters, Lemkin was gaunt, with greying hair and softly spoken.

The influence of Lemkin on the genocide convention is very marked but the convention had a difficult passage through the assembly with some delegates claiming that at the end of it the convention was of symbolic significance and tyrants were unlikely to be dissuaded by it. But it did define and denounce genocide and established it as a crime under international law and a matter of international concern.

On the 50th anniversary of the genocide convention, it is well to remember that human rights violations differ in degree. Lemkin believed there were two clear cases of genocide this century and that the Holocaust could be compared only with the massacres of the Armenians by the Turks in 1915-1916.

Lemkin noted the similarities in each: in Turkey there had clearly existed a deliberate and methodical government policy aimed at the extermination of an innocent minority and not, as Turkish apologists have claimed, a wartime security measure against a treasonous group.

One more genocide is now added to this century - the attempt to exterminate the Tutsi in Rwanda in 1994: the first genocide to be officially recognised by the UN since the Holocaust.

There are telling similarities with the century's three genocides: a pervasive racial ideology and propaganda; a dependence on military security; monolithic political parties, and one last, vital ingredient - an assurance that the interference of other nations is at a minimum.

THE third genocide of the 20th century, that in Rwanda, has seen one million people killed in a deliberate, public and political campaign. It was a crime of mass complicity. The murders were directed by central government.

A militia of the unemployed was trained to kill 1,000 people every 20 minutes. Local administrators organised the disposal of bodies in garbage trucks.

The slaughter continued, unhindered, for three months. Many civilians bled to death - mutilated with the simplest of agricultural tools - the machete.

The rate of extermination of people was five times faster than that of the Nazis. It was human loss on an unimaginable scale.

It has taken almost five years for this genocide, contested at first by the western powers, to be fully recognised as the third clear case of the crime this century.

What the genocide in Rwanda has proved is how far we are from even beginning to understand the promise of "never again" enshrined in the convention to prevent and punish the crime, adopted 50 years ago.

Linda Melvern is a British author and journalist whose most recent book, The Ultimate Crime, a history of the UN, was published by Allison and Busby, London, in 1995. She is currently working on a book to explain the exact circumstances of the genocide in Rwanda.

On Wednesday, the Irish Times will publish a special pull-out supplement to mark the 50th anniversary of the UN Declaration of Human Rights.