|[kɑt]||cot, caught *|
This symbol is called "script A", because it's the kind of A you would make when hand-writing. The kind of A that looks like it's typewritten, [a], is a different IPA symbol representing a different sound (you can see it as part of [aj] and [aw]).
You will occasionally see this symbol printed or typed as [a] by people who are too lazy to make it [ɑ]. They are bad, bad people. Never imitate them.
(* If you don't think cot and caught sound the same or that law and father have the same vowel, then you're not from Manitoba, are you? A fuller explanation can be found on the open-o page, but for now, just relax.)