Someone or something that closes.
In our organization, the VP of Sales usually acts as the closer.
Someone or something that concludes.
The DJ chose a fantastic track as his closer at the end of the night.
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. See Wikipedia:closer (baseball)
They brought their closer in for the ninth.