A nibble from a cat means many things, but it is often considered a “love bite” in which the cat is telling the person that it is pleased or happy. Cats often communicate through body language. This is why cats rub themselves against people, lick and even bite.
A nibble from a cat does not always mean that they are pleased. It is important for the person who is being nibbled to read the situation. Sometimes cats use nibbles to indicate that they are being over-stimulated. A perfect example is when a cat is being rubbed in the area right before their tail on their lower back. This is an extremely sensitive area for most cats. If a cat nibbles while being rubbed in this area, the cat is more than likely saying that enough is enough.
Besides trying to show affection and over-stimulation, a nibble is sometimes used by cats when they feel playful. It is common for cats to lick and bite when they play. Younger cats learn their boundaries while playing with their mothers. When a kitten starts playing too rough, the adult cat will stop playing. This is a sign for the kitten that it was playing too rough.