A REME Tradesman who has undergone Artificer training. Two years at sunny Bordon where you come out with a HND in Engineering (can someone confirm the qualification please?).
You also jump straight to Staff Sergeant and can progress onto become an AQMS, an ASM and are a shoe in for LE commisioning.
Most Tiffies prefer to be called 'Tiff' as opposed to Staff.
Similar term applies to a Royal Navy Artificer.