Since this word is made up of a single kanji, it probably uses the kun'yomi reading. You did not learn this meaning, so here's a mnemonic to help you to remember:
There are lots of whirlpools at the uni zoo (うず). Unis really like being spun around in whirlpools, so when you go to the zoo to see them look out for the tank full of them!
Why do whirlpools appear in the ocean?