Lateral masking is a problem for the human visual perception of identical or similar entities in close proximity. This can be illustrated by the difficulty of counting the vertical bars of a barcode.
In linguistics lateral masking refers to the interference a letter has on its neighbor[1]. This is a problem readers encounter when reading a word. The identity of a letter in the middle of a word is obscured by the presence of its neighboring letters.
Lateral masking is also a problem in orthography design[2]. A readable orthography will avoid situations in which a reader is faced with severe lateral masking.
Roberts, David (2008). L'orthographe du ton en kabiyè au banc d'essai. INALCO. Paris [1]