Guildmage

Each of the Ten Guilds have very different hierarchies and ranks, but one, and perhaps the only, common ground between all of them are the existence of their Guildmages.
The term "Guildmage" is essentially shorthand for a member of a Guild that is capable of using that Guild's style of magic. Azorius Hussars are trained in using support, detainment, and bolstering magic. Members of the Golgari assassination group known as the Ochran are skilled alchemists and experts in hexes. Dimir Thought Thieves can obviously steal a small memory from their target without them being any the wiser. All of these examples would be considered Guildmages.