A crafting profession is a trade-oriented skill players learn in order to gather, make, or otherwise enhance items.
Professions are learned from a specific trainer or books after a specific mastery level (such as Runecloth bandages). Most professions, with the exception of Runeforging (available only to Death Knights) can be learned by any race or class.
Specific trade skills within a profession allow a player to craft a specific types of items or add enhancements to items, such as Cobrahide Leg Armor for example. These skills (or recipes) are learned from the profession's trainers, they are dropped from recipes or are obtained as a result of a quest for that profession.