Cosplay is short for costume-roleplaying. It is when regular folks (most of the time, non-professionals) dress up as their favorite anime, game, etc. characters. This list is for the best of them.
Samus Aran is the heroine in the popular game franchise Metroid.
Note: The name "Metroid" actually refers to the parasitic life forms that can absorb all types of energy and have natural resistances to almost all conventional weapons except for ice beams (go figure).
From Street Fighter 2
Cosplay is from halo. The production quality is unreal, I'm not sure if this is from a professional outfit or not.