The Polish word for Polish person is Polak, which became Polack when Anglicized — until we all hopped on the euphemism treadmill:
The noun Polack, in the contemporary English language, is a derogatory reference to a person of Polish descent. It is an Anglicisation of the Polish language word Polak, which means a Polish male person (feminine being Polka) with a neutral connotation. However, the English loanword “Polack” (note, the spelling difference which does not appear in Polish) is considered an ethnic slur in the US and the UK, and therefore is inherently insulting in nearly all modern usages.
The “correct” modern term is Pole — for now.