In the first serial, "An Unearthly Child", Susan Foreman claims, "I made up the name TARDIS from the initials, Time And Relative Dimension In Space."
In "The Name of the Doctor", the guard watching the monitor showing the Doctor sneaking about the repair shop says, "What kind of idiot would steal a faulty TARDIS?"
Was this simply a writing error or do all Gallifreyans call them TARDISes? Assuming it is a mistake, this would mean the Doctor's TARDIS is the only "TARDIS". However, I recall that other characters had time machines referred to as TARDIS, e.g. the Rani and the Master.
Wikipedia states the TARDIS is a Type 40 TT capsule (TT meaning Time Travel). Should the guard not have stated, "What kind of idiot would steal a faulty Type 40? Also, why would other time lords and ladies call their time machines (whatever model) TARDIS?