What’s the difference between an arm and a tentacle, in regards to cephalopods?

The difference is cephalopod arms have suckers all the way along their length, but tentacles only have suckers at the end (except for nautilus tentacles, which have no suckers).

Arm:

Tentacle:

So octopus have 8 arms and no tentacles, squid and cuttlefish have 8 arms and 2 tentacles (except female cuttlefish, which have 6 arms), and nautilus have around 90 tentacles and no arms.