The Plug Ins effect for Final Cut Pro are divided to three types: Filters, Transitions and Generators.
Filters are effects which modify clips
Transitions are effects that merge two clips in edit points
Generators are effects which produce new clips
Currently the set of 30 PlugIns is combined of 13 filters, 9 transitions and 8 generators. Some of the PlugIns aim to simplify editing and compositing with Final cut pro, and some provide new visual capabilities.