Does it mean anything that my dog nibbles on people?

My black lab LOVES to nibble on people.. mainly me and my boyfriend. Granted him and my boyfriend love to rough house but he does it when we wake up, when we're just sitting there watching TV. Basically all the time. Now I just want to know what this...

means? Does it even have some special meaning?

Thanks.

The dog is playing the way it knows how to play instinctually. This can also pose a problem though should he play a little too rough and you should pull away from the nibbling causing a tear in the skin. If this is a problem for you or should you plan to expose your dog to anyone else that might not like this behavior then I would strongly suggest training the habit out of him.

Puppies tend to nip a lot in play, and their pointy little milk teeth can easily puncture skin. Aside from the pain factor, a nipping puppy that does not learn to curb this behaviour will often grow into a dog that uses his mouth for rough play. While the intention is benign, the damage can be great, and a dog bite, is a dog bite according to the law. By starting young, you can easily teach your puppy or young adult that mouthing is just not acceptable.

The most effective method is the Yelp and Shun method.
Try yelping in a loud high-pitched voice when he bites. As soon as he lets go, turn away from him, and refuse to play any longer. This mimics the behaviour that his pack-mates would use when he gets out of line. Before long, your puppy will learn that using his mouth on his people cause his people to turn away from him.

Other methods that may work with your dog are:

Trade. Trade me that arm for this toy, and you'll recieve plenty of praise when your chewing is redirected to an appropriate outlet.

Instant Muzzle. When your puppy grabs your hand, flip it around on him and wrap it around his muzzle, holding his mouth closed for a few seconds. This is not a pleasant experience, and many dogs often get the hint fairly quickly.

Play biting can evolve into a serious problem, so it is best to find out which method works, and employ it to teach your dog appropriate play.