A gaiter is a complete boot, not just a slipover piece.
The Henri Lloyd version of the gaiter is designed primarily for water use, although they can be an asset in many situations related to camping and hiking.
This type of gaiter is intended to protect the feet and lower portion of the leg from any dangers associated with water, snow, or dangerous terrain.
The term gaiter refers to a piece of clothing intended to protect sensitive areas of the body.
Some people use the terms gaiter and leggings interchangeably.
Henri Lloyd also sells a type of gaiter called the Racer boot.