What does jerk bait mean?

Jerk bait is a bait or lure that shudders under the water to atract fish.

Sorry, you're wrong. 'Jerk bait' is actually a method of fishing (for predators, usually pike or similar) which utilises a short stiff rod and artificial lres known as jerk-baits. Action / movement is imparted to the lures by alternatly jerking the rod tip and winding the reel, which causes the bait (often quite large and garish) to dart forwards / side to side / up and down in an erratic manner that is attractive to the fish, causing them to attck the bait.

It is a method typically used when either a/ you expect to encounter larger than average fish or b/ you wish to try and selectively attract the larger specimens in the locality.