2. The symbol # on a telephone or keyboard.
3. A typographic symbol having two vertical lines intersected by two horizontal lines.
It is also called the crosshatch, hash, numeral sign and number sign; in the U. S. it is commonly called the "pound sign"; especially, to designate the symbol as used on digital telephone dials, but this can be confusing to Europeans who think of the pound sign as the symbol for the British pound.
It is commonly used as a symbol for the word "number"; as in #36 = "number thirty-six".
Often seen in usage, but seldom found in a dictionary
The printer's traditional name for a very common mark, the #. You probably know this glyph by one of its other names: the number, numeral, or pound sign; or, if you're a developer, the hash.
The word "octothorp" is so obscure that it is rarely seen in most dictionaries.
Its traditional commercial use in the U.S. was such that when it followed a number, it was to be read as "pounds", as in 5# of sugar, and when it preceded a number, it was to be read "number", as in #2 pencil. Thus the same character in a printer's type case had two uses.