"Sittin" is a colloquial contraction of the word "sitting." It often refers to the act of being seated or resting in a relaxed position. Full definition
I know a fair amount about fitness and just being healthy in general, but at the same time I love just sittin on my couch with a good game for hours: D (videogamerdating.com)
So today we're front porch sittin» with a nice glass of Malbec in hand. (lexwhatwear.com)
Im a woman that has no time for childish sittin in the shadow games any more. (doulike.com)