The Scout Ship is a short range Yautja Spacecraft which is usually connected to a Mother Ship. Scout Ships have three external thrusters and a large blade on the belly of the vessel. The hull of the Scout Ship was not very strong against Yautja technology, with a single hit from a Plasmacaster being able to created a fairly large hole in the side of the ship. Scout Ships usually had a fairly large Trophy Room used for displaying any Trophies obtained on Hunts. Scout Ships also possessed holographic technology capable of displaying holograms of nearby planets likely to be used as a site for a Hunt. Scout Ships also contains a storage room for captive Facehuggers. Scout Ships were used to drop off yautja hunters in close proximity of a planet.
In AVP: Evolution a Mother Ship (clearly depicted in the loading screen to Predator Mission 2 - Predator Ship and also possessing a Trophy Room heavily based on the one seen in Predator 2) is incorrectly referred to as a Scout Ship.
Why Scout Ships detach from a Mother Ship and then deploy a Yautja to a planet instead of the Mother Ship itself just going to the planet and deploying the pod (which they have been seen using) is unclear, although it could be that the Mother Ship deploys numerous Yautja to Hunt at the same time, making it faster to send them in separate ships.
The scene from the beginning of Aliens vs. Predator: Requiem showing a Facehugger in a tube aboard the Scout Ship lunging at the camera is an obvious reference to the similar scene in Aliens where a Facehugger in a tube lunges at Burke in an identical manner.