An anchor bolt is a bolt or threaded stud cast into a concrete pour. The threaded end protrudes from the cured concrete, ready for a base plate or footplate post to bolt down onto. The buried end is bent (an L-bolt) or has an enlarged head or washer (a J-bolt or headed anchor) to lock it into the concrete against pull-out.
Anchor bolts are placed before the concrete pour, with a template that holds them in the right pattern at the right height. Get the template wrong and the base plate won't fit.
For gate posts on a new concrete pad, cast anchors give the strongest possible bolt-down because the bolt is fully embedded in the concrete. For retrofit on an existing pad (no pour planned), use chemical anchors or dynabolts instead.