They want guys who have flown the aircraft within the last 6 months, type-rated, with preferably 3 landings in the last 6 months. (Not an absolute, but most of the ads say this).

The "100 hours PIC" would be for say, a guy who is a 767 Capt with 15,000 hours and 6000 of it PIC on the 767, but trying for a 747 Capt slot where he has only 100 hours of 747 Capt time.