Twosquare

Twosquare is a term used across multiple disciplines and domains; there is no single canonical subject known as "twosquare." The meaning depends on the context, and the term can refer to mathematical concepts, cryptographic methods, or as a proper name.

In classical cryptography, the two-square cipher is a digraphic substitution cipher that uses two square matrices, typically 5x5, filled with letters (commonly merging I and J). Plaintext digraphs are encoded into ciphertext digraphs by combining the coordinates from the two squares. It is related to the Playfair cipher as a cousin technique and was widely discussed in historical cryptography literature.

In a geometric or mathematical context, "two-square" can describe a square with side length two units, i.e., a 2x2 square, or more generally indicate a grouping of four equal cells in a grid. In tiling or combinatorial grid problems, a two-square block is a 2x2 tile.

In contemporary software, media, or branding, "twosquare" may be used as a proper noun for products, projects, companies, or usernames. Because these usages are diverse, specifying the domain is necessary to identify the intended referent.

See also two-square cipher, Playfair cipher, 2x2 square, grid, tiling.