Paul; I think he means combination punching - a rapid seies of strikes to the same general target.
Chris: Irimi means to 'enter'. It is not a technique in itself, rather a direction of movement. In Irimi, you move in
towards your attacker, depending on circumstance. For instance; in what Lynn said; as the punch(es) come in; you step offline - i.e. to the side; out of the direct path of the attack, then step inside the attack - irimi. This would in this case have you closing in to the attacker's elbow; a prime position for technique.
An interesting point - we just held a joint training day between ourselves and the Karate dojo in the same building. most of the Karate guys - and most of us as well - thought the combination attacks that make Karate so effective would overcome the movement of Aikido. we were all shocked - and not a bit pleased - when our Sensei, Jill did almost exactly what Lynn suggested here, with tenkan instead of irimi - she followed the Karate sensei's punch in with Tenkan (moving off-line and turning to the attacker's line) and flipped him to the floor with an almost casual pull on his shoulders. Neat.