Non aggresive tail wagging

Question
I have a new adopted cat ( from the local vet) 15 months old. He is playful and affectionate. He sometimes bites (playfully) but his tail is always wagging (when he is on the couch,walking around or sitting) I don't understand this. We (my wife and I) have had cats before and none of them ever displayed this tail wagging thing.
The new cat was adopted to replace our old cat (18 years) that had to be put to sleep 2 months ago.

Answer
Bill,

I am assuming he is neutered.  if not, you need to do that ASAP!

Tail wagging can mean lots of things in cats, depending on whether they are flicking it from side to side (excitement and/or stalking/hunting and/or annoyance {but mostly if just the tail tip is twitching}).  If the cat is wiggling his tail (kind of along the vertical), he may be thinking of spraying.  If he is neutered, he probably will not spray, whereas if he is whole, he very well might spray with that behavior.

If nothing untoward is happening, I would chalk it up to a behavioral anomaly and enjoy his differences.

By the way, on playful biting, this should be discouraged.  If when petting or stroking, he begins this behavior, it is time to put him down and walk away.  If he is whole, neutering may help as this could be a sign of alpha male dominance as a whole cat!

Best regards... Norm.