One of my friends getting this message when he is trying to login on this forum.
you are banned from posting or sending personal messages on this forum.
Intrusive and off-topic ad (3 days)
What does it means? Is he permanently banned or he is banned for 3 days?
He's banned for 3 days, presumably for posting advertisements in unrelated threads. You should probably let him know the reason if he hasn't figured it out (though it should be obvious from the ban reason) so that he doesn't do it again and get banned for longer once the current ban expires.