1) Letting loose with a friend or someone who is cool.
2) To chill in someplace cool
or with someone cool
: tight, awesome
: to be relieved from tension or strain
Person 1: So, what are you up to tonight?
Person 2: I don't know. I might illax with _____
Person 1: What've you been doing all summer?
Person 2: Nothing much... just illaxin' and stuff.