Arab leaders are expected to renew an offer to normalise relations with Israel, if it withdraws from all occupied land.
Libya's leader was the first to arrive in the Algerian capital
On the opening day of the Arab League summit in Algiers, President Abdelaziz Bouteflika called for the UN to issue a definition of terrorism.
He said only then could "an alliance between civilisations" be agreed that would protect all sides from terrorism. Only 13 of the 22 Arab leaders are attending the two-day summit.
Jordan's King Abdullah, Saudi Arabia's Crown Prince Abdullah, Yemeni President Ali Abdullah Saleh and Lebanese President Emile Lahoud are among those missing the summit.
The Arab leaders meeting in the Algerian capital for their annual summit are expected to renew a three-year-old offer of peace to Israel.
The basic outline of the plan, originally proposed by Saudi Arabia, calls on the Jewish state to withdraw from Arab land it occupied in 1967 in exchange for normal relations with all Arab states. The plan was rejected by Israel in 2002.
Foreign ministers who blocked a more sweeping Jordanian proposal seem to have been wary the Arabs will appear to be making concessions without getting anything in return.
Jordan wanted to build on the improvement of atmosphere in the region, following signs that both Israel and the Palestinians were prepared to suspend violent actions.
Kinds of terrorism
Mr Bouteflika told the summit: "In this world, everyone is fighting its terrorism. Some are fighting Islam, others make it an excuse to invade countries."
"There should be a clear definition of terrorism that everyone in the United Nations can agree on.
"Only then we can reach an alliance between civilizations which will protect both from the dangers."
Arab governments have for a long time tried to resist the definition by Western governments, especially the United States, of Palestinian and Lebanese militant groups as terrorists.
Many Arabs view armed struggle against occupying forces in Israel or Iraq as legitimate resistance.
Caution on Syria
The Arab leaders are also expected to recycle old resolutions expressing support for Syria and opposition to US sanctions against it.
They will, however, steer clear of any formal discussion of the Syrian presence in Lebanon and the crisis which followed the assassination of former Lebanese Prime Minister Rafik Hariri.
BBC Cairo correspondent Heba Saleh says Arab public opinion has long learned not to expect anything much of Arab summits except perhaps public spats between leaders.
This year 13 heads of state are expected to stay away - though Libyan leader Muammar Gaddafi, who stormed out of the last summit, was the first to arrive in Algiers.
European Union foreign policy chief Javier Solana is also attending. He said he was in Algiers in the hope of helping to advance the Middle East peace process.
UN Secretary General Kofi Annan, Spanish Prime Minister Jose Luis Rodriguez Zapatero and French Foreign Michel Barnier are also scheduled to attend parts of the summit.