The West Bank is a chunk of land east of Israel. It’s home to nearly three million Palestinians, and would make up the heart of any Palestinian state. Israel took control of it in 1967 and has allowed Jewish settlers to move in, but Palestinians (and most of the international community) consider it illegally occupied Palestinian land.
In 1967, Israel fought a war with Egypt, Syria, and Jordan. Israel fired the first shot, but claims it was preempting an imminent Egyptian attack; Arabs disagree, casting Israel as an aggressor. In six days, Israel routed the Arab powers, taking the West Bank and East Jerusalem from Jordan.
Israel has controlled the West Bank since the Six-Day War (as it’s called). For many Jews, this is wonderful news in theory: the West Bank was the heartland of the ancient Jewish state. It’s home to many Jewish holy sites, like the Cave of the Patriarchs in Hebron, that Jews were previously cut off from. In practice, Israeli control of the West Bank means military administration of a territory full of Palestinians who aren’t exactly excited about living under Israeli authority.
The border between Israel and the West Bank would probably have to change in any peace deal. There are about 500,000 Jewish settlers living in the West Bank, many of whom live near the border with Israel proper. In a two-state deal, some of these settlers would have to leave the West Bank, while some border settlements would become Israeli land. In exchange, Israel would give over some of its territory to Palestine. These would be called “land swaps.” No set of Israeli and Palestinian leaders have agreed on precisely where to draw the border.