To initiate conversation, the second a person logs into their IM.
X)waiting for sign in
by Silent0809 February 19, 2009
1 more definition
When someone jumps on you immediately when you sign in to messenger or another instant messaging application.
I *just* wanted to check my emails and go to bed when Steve IMpounced me and I had to chat for another half hour!
by jbng October 07, 2007