The election of 1824 was decided in the House of Representatives. The candidates were John Quincy Adams, Andrew Jackson, and Henry Clay. When the election day came, Andrew Jackson won the plurality of the popular vote and the electoral college, John Quincy Adams came in second and Henry Clay was in fourth place after Crawford.
The problem was that the US Constitution dictates that a candidate needs to win a majority in the electoral college but no one did that, so the House of Representatives needed to decide the matter.
In January 1824 Quincy invited Henry Clay to visit him at his residence and in February Clay made it known that he supported Adams and thanks to his influence, Adams won the vote of the House of Representatives and was elected President of the US.
Andrew Jackson denounced the election as a corrupt bargain because Clay sold his influence to Adams so he could be secretary of state and increase his own chance of being president one day.