“Bite inhibition” is somewhat of a misleading phrase. The word “inhibition” normally means something that restrains, blocks or suppresses. That is only partially true for a dog engaging in bite inhibition.
Dogs and cats have much more control over biting than you probably realize. They don’t just bite down on something with the same force each time. That is expected as the dog eats, needing to crunch down with force on a hard biscuit, for example, but with less energy for a tender morsel of dog chow. But dogs use this same adjustment when biting others -- including humans and different dogs.
Evelyn Pang and Hilary Louie, authors of the book Good Dog!: Kids Teach Kids About Dog Behavior and Training, explain that bite inhibition is when your dog bites down on you, without pushing in with its teeth. Essentially, it is mouthing or nipping you. Puppies do this a lot, nipping at your heels and other places. In the case of puppies, the young dogs are often just exploring their environment in a playful way. Nipping is one way to test the waters in terms of using their teeth and mouth and seeing how others will react.
For older dogs that bite in this seemingly harmless way, the dog is giving you a warning. You might be brushing the dog in an uncomfortable way or doing something else that is painful or stressful. If you do not heed the bite inhibition warning, the next bite will not be so gentle. If your dog nips for seemingly no reason, however, you might schedule a veterinary visit, as cranky dogs may have an underlying health issue. Your dog could also need a training refresher course to prevent the painless bites from turning into something more serious.