What is the meaning of Closer?

comparative form of close: more close

Within a shorter distance.

Someone or something that closes.

Someone or something that concludes.

Synonym of close (the point at the end of a sales pitch when the consumer is asked to buy)

The last stone in a horizontal course, if smaller than the others; a piece of brick finishing a course.

A relief pitcher who specializes in getting the last three outs of the game.

English Wikipedia has an article on:
Wikipedia

A horse that performs best toward the end of a race.

Source: wiktionary.org