1. In learning theory, the acquiring and learning of a new skill by observing and imitating that behaviour being performed by another individual.
2. In behaviour modification, a treatment procedure whereby the therapist or another significant person presents (models) the target behaviour which the learner is to imitate and make part of his repertoire.
3. A continuous process by which a bone is altered in size and shape during its growth by resorption and formation of bone at different sites and rates.