Autoclave tape is tape you put on a package before you put it in an autoclave (an autoclave being an oven, basically, which heats medical instuments under extreme pressure to sterilize them). The tape has special strips running through it, so that after it has been cooked in the autoclave, the strips turn black and everyone knows the instuments are safe for surgery.
‘Tape you use on an autoclave’ indeed. Hmph. 
-Henry