Whats the difference between a 8 set, Bid Set, 5 set, etc. when buying a floor plan for a house?

Question:Hi! ive been looking at house plans latly and when i press Purchese this plan you have to choose between;
Bid Set
Five Set Package
Eight Set Package
Vellums - Single Use
and
CAD File - Single Use

What is the difference between all of these choices and which do you recomend!
Hope U Can Help!

Answers:
Bid Set - Single set of plans without Architect signatures for plan department

Five Set Package - Five sets as above but may include signatures for approvals

Eight Set Package - Eight sets as above but may include signatures for approvals

Vellums - Single set of drawing. Suitable for blue line reproduction.

CAD File - Electronic File openable by Auto CAD drafting program.

The CAD Drawings are the most versatile format but you need the program to open them.