The Electoral College was set up by the US founding fathers as a compromise between allowing Congress and the people to elect the president.
The electors are mostly elected officials or party functionaries whose names are not on the ballot. They are generally unknown to the public apart from one or two exceptions such as former President Bill Clinton, who was a New York elector in 2016.
There are 538 electors in all, one for each member of Congress. A candidate needs to take at least 270 electoral votes – half of the total plus one – to win the White House.
In 2016, Donald Trump won 306 electors from 30 states.
If no candidate reaches 270 in the Electoral College, the House of Representatives must vote on the next president.