UHF RFID

Ultra High Frequency RFID

This is the tag everyone is talking about when they say "RFID". Unless they are talking about something else.

And, when they say UHF -- they really mean Gen2 RFID.

Other things they may be talking about:

HF - Generally, proprietary and old-school. Still used, but not very interesting.

LF - See HF.

Active - Can be useful if you need RTLS (Real Time Location) -- but, most people don't want to spend $50 - $100 per RFID tag to find stuff.