mask
1. In communications systems, to obscure, hide, or otherwise prevent information from being derived from a signal.
Note 1: Masking is usually the result of interaction with another signal, such as noise, static, jamming, or other forms of interference.
Note 2: Masking is not synonymous with erasing or deleting.
2. In computing and data processing systems, a pattern of bits that can be used to retain or suppress segments of another pattern of bits. [From Weik ’89]