As others have stated, an informal greeting meaning "Hello, how are you?". But the true spelling should be Trix (with a capital T) because of its origin, which no one seems to know: It was (still) an informal greeting, started in the early 20th century; but the entire phrase was "How are Trixie and the kids?"... basically asking how one's family was doing. Trixie was short for Beatrix, or Beatrice (a popular female name of the era) and came to be known as slang for "the wife". Over time the phrase was shortened to simply "How's Trix?"
"Hey Rob, long time no see. How's tricks?" ... "Doing well Joe, thanks." (Incorrectly spelled there on purpose to satisfy UD - use Trix)