Bulk vs. Published Air

Airlines offer pricing referred to as "Bulk" airfare through certain tour operators when purchased with a hotel stay. The advantages of a bulk are fare are several.

1) They are often (but not always) less expensive.
2) They don't require full payment at time of booking (unless booked close in).
3) They aren't always completely non refundable.

Published airfares are the kind you usually buy. They are instant purchase, non refundable, hard to change, etc.