[JBotAlan]

Bulletin Board System: I never actually logged onto one of these, but the way I understand it, they were servers that you could dial (yes, a modem over a telephone line was high-tech) into to...chat with other people? Like I said, I never used one, so I have no idea. I would guess it's somewhat a precursor to our MUDs.
Mainframe: Need I say any more? I cringe when I hear people use this word in a modern sentence. (What is a mainframe, anyway?)
Cassette tape: old to me, but new to my parents.
Acoustic pickup (?): Before modems connected to the phone line, you would dial the BBS's number, then put the phone in the pickup to link it to the computer.

Correct me on these if I got them wrong--I don't know some of them.