French term (edited): carr�

In the good old days, taps had a square bit at the top of the spindle, and a threaded axial hole in the spindle. The tap handle fitted over and mated with the square bit, and a screw secured it. With time, and a good dose of abuse, the square edges wore, were flattened, and the tap handle would spin round uselessly ...

These days, what with more sophisticated machining, tap spindles are more often than not star-shaped, giving a more positive engagement.

Whether in your case they hide the handle under lock and key or simply have a square wrench/spanner remains to be seen.

Of course, when they say "carré" they might actually mean "budget-lock type", since this can cover any kind of square-in-round, triangle-in-round operating mechanism, i.e. the sort of lock on train toilet doors, that only the conductor can open when locked, with a special key. The advantage of a triangular tap spindle would be that it would be more difficult to turn with an ordinary spanner than a square one ....

So you might want to play safe with "specially-shaped spindle" or "specially shaped operating mechanism", "tamper-proof operating mechanism" (if one is optimistic ...)