Irimi is a term most often used in Aikido. Here are some pretty good Aikido explanation of it (well, Irimi-Nage):http://www.youtube.com/watch?v=mt4ts-rOpyMhttp://www.aikiweb.com/forums/showthread.php?p=205189
Aside from the physical movements associated with Irimi, I was taught it was almost like a pre-empt. movement. For instance, you seen someone moving to grab a tanto (knife) from their belt. You "enter" into their "sphere" (body space, for want of a cruder explanation) and seixe their wrist before they take out the knife. Although I "entered" his space, and grabbed his wrist, he attacked first due to his intent (trying to take out a knife). It is a key idea of Aiki as I understand it.
It's hard to explain without starting another thread entirely! Would be a good discussion for the Aikido forum!
Don't know if that is the term you were looking for overall though???