Meaning

noun the mechanical advantage gained by being in a position to use a lever

noun strategic advantage; power to act effectively

noun investing with borrowed money as a way to amplify potential gains (at the risk of greater losses)

originFrom lever + -age. The verb likely comes from martial arts/judo usage, where one would "use an opponent's leverage (i.e. their weight, height, centre of balance, etc.)" against them in order to defeat them.

Etymology from Wiktionary, CC BY-SA 3.0