Hash mark is the commonly used term for the pound sign or the number sign (#). This symbol has many other synonyms, including octothorpe, crosshatch, grid, tic-tac-toe board, and sharp sign. The octothorpe is the name given specifically to the symbol on telephones used to indicate pound or number calls. The crosshatch name comes from the lines crossing each other to create a grid pattern. The grid is used to indicate the layout of structures, graphs, and tables. The tic-tac-toe board is a term commonly used in games, while the sharp sign is used in music notation to indicate a note should be increased by a semitone.