Used to give an estimate with a small uncertainty in either direction, usually associated with time or distances.
It'll take me 3 weeks, give or take a day or two.
The liquor store is a kilometer away, give or take a couple of hundred metres.
Literally, to poke someone. Typically this is done over an IM client.
Part of the old school emote family (yeah, before lolcats).
Like anything enclosed in asterisks, *poke* is performing the action of poking the person you send it to.
Largely replaced, in modern context, with "/e", "/me" or "/em" (emote) preceding the action.
Bro: Hey Dude, what's up?
<Long period of silence>
Bro: *Poke* Oi! Wake up!
Dude: ouch! Sorry was doing other stuff!