The Occupied Territories are the West Bank, East Jerusalem, the Gaza Strip, and the Golan Heights. "Occupied Palestinian Territories" or simply "Palestinian territories" is sometimes used to refer to the West Bank, East Jerusalem and the Gaza Strip, excluding the (Syrian) Golan Heights.
On June 5, 1967, Israel launched what it claimed to be a preemptive attack on Egypt, citing Egypt's announced closure of the Straits of Tiran (the opening from the Gulf of Aqaba to the Red Sea) to Israeli shipping, and other provocations. Israeli military and political leaders later admitted that they had not, in fact, genuinely feared attack, and had no doubt about Israel's vast military superiority over its neighbors.
By the time fighting ended six days later, Israel had seized Egypt's Sinai Peninsula, the Gaza Strip (which had been under Egyptian administration since 1948), the West Bank (which had been under Jordanian rule since 1948), and Syria's Golan Heights. (The Sinai Peninsula was returned to Egypt after the 1979 peace treaty between Egypt and Israel.)
"Occupation" is a legal status in international law, not just a description of the forceful means by which Israel has controlled the territories it seized in 1967. Although Israeli diplomats contest the designation of the territories as "occupied," and describe them as merely "administered" by Israel, there is no such status in international law.
All competent legal authorities - including the International Court of Justice, the United Nations Security Council and Israel's own Supreme Court -- recognize the Gaza Strip, West Bank, and Golan Heights as occupied territories.
International law imposes obligations and limitations on the actions of an occupying power, and the Charter of the United Nations bars acquisition of territory by war. Thus Israel has never had any legal rights of sovereignty over any of the lands it took in 1967, and never had any right to settle its own citizens there.
The Gaza Strip continues to be "occupied" notwithstanding Israel's withdrawal of settlers and redeployment of troops outside the Strip in 2005. Effective control is the measure of "occupation" in international law, and Israel clearly continues to control the coast, borders and airspace of the Strip, claims the right to reinvade at will, and provides Gazans their water, electricity, and other vital services.