The Constitution provides two ways that a candidate may be elected President: First, he or she can obtain a majority of electors during the meetings of the Electoral College. There are currently 538 electors, so it takes 270 electors to win an election in this way. This is how we are used to seeing Presidents elected!
But what if no one gets a majority? If no candidate obtains at least 270 electors, then the Constitution provides a back-up election procedure: an election in the House of Representatives. This secondary election process is commonly referred to as the House contingent election.
The last time we held a House contingent election was after the 1824 election, so it’s been a while!