what does ccmt mean

It's an ISO standard, although I don't know which one:-

C= 80 degree rhombic shape C=7 degree relief angle M=tolerances on corner height, thickness and Inscribed circle diameter T=with a partially cylindrical double sided 40 degree (bottom) and 60 degree (top) tapered fixing hole. Also with a single sided chip breaker.

:-)

There is lot's more for the different types of insert but my typing finger would wear out. If you get a too catalogue ( e.g.

Mark Rand RTFM