(1) A structure made by sessile marine invertebrates knows as Corals, usually mostly by small polyped scleractinian corals such as Acropora or Montipora.
(2) A slang term for Marijuana: Cannabis
(3) A term meaning pulling on something forcefully.
(1) As Bob swam over the Acropora reef, he couldn't help but notice the abundance of Blue reef chromis.
(2) "Hey, I heard the cops arrested Jhonny because he was selling reef. I can't believe he would do such a thing."
(3) "Stop reefing on that pencil, or you will break it"