To summarize here all the answers that people gave in comments:

1) There seems not to be a standard notation/terminology for  $\bar{A}\setminus A$ in the literature.

2) Points in $\bar{A}\setminus A$ can be referred to as "limit/closure points not in $A$" or "external limit/closure points".

3) $\bar{A}\setminus A$ is different in general than the boundary/frontier of $A$ which is defined as $\bar{A}\setminus int(A)$, where $int(A)$ is the interior of $A$.