1. in evolutionary genetics, the containment of variation of certain characters within narrow bounds so that expression of underlying genetic variation is repressed. It is a developmental mechanism that maintains a constant phenotype over a range of different environments in which the organism might normally occur.

2. in neuroscience, the hypothetical process by which repeated use of a neural pathway leads to greater ease of transmission of impulses and hence its establishment as permanent.

3. in psychology, the channeling by an organism of its needs into fixed patterns of gratification, for example, food or recreational preferences.