what does the word bracket mean?

1. (n) A piece of punctuation, one of a pair of square three sided figures which enclose, usually, an interpolation into a quotation. [This is enclosed by brackets]

2. (n) Figuratively, a range of things defined by limits like brackets, especially an "income bracket"

3. (v) To place on either side of something. Used especially in artillery spotting.

4. (n) A right angled support for a shelf, attached both to a wall and the bottom of the shelf.