LATERAL OPENING is a term used in architecture to describe the openings between two walls that are parallel to each other. The three solutions for this term are TRI (3 letters), UNI (3 letters), and EQUI (4 letters). TRI stands for triangular, UNI stands for unidirectional, and EQUI stands for equilateral. These terms refer to the shape of the OPENING between the two walls. Triangular openings have three sides, unidirectional openings have one side, and equilateral openings have all sides equal in length.