Here are some thoughts taken from other forums about that topic:
"Well, passive is something that happens without doing it, so maybe it talks about your character attitude ? Or your character background story, as it's passive - always effecting your RP."
"The RP that happens around you, character attitude, accent, hand movements, fighting styles etc. Active-the RP you do, the /me's you write etc."
Passive roleplay helps you improve your roleplaying skills and develop your character's habbits, emotions and activities. You can roleplay having a pet, riding a skateboard, knowing a martial art, being fat, thin, and on and on. It's roleplaying with objects and items that aren't necessarily there, but you're using your imagination to make things interesting.
In one of my guides you can find out about roleplaying hobbies and sports. This is also passive roleplay. You can roleplay playing football, playing basketball or almost anything that's not possible to be done script-wise.
You can roleplay hiding your keys in your shoe, hiding your money inside your cigarette pack, etc.
It's roleplaying with objects and items that aren't necessarily there, but you're using your imagination to make things interesting. For example you can roleplay placing your drugs and selling them in Pizza Stacks bags,
that would help you not to drag attention from the cops, you could passive roleplay that your phone is being tracked and buy new phones every few days.