octothorp

(an explanation of what it is and where it came from)

octothorp, octothorpe
1. The official name for the numbers sign which looks like: #
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.

"Otherwise known as the numeral sign. It has also been used as a symbol for the pound avoirdupois, but this usage is now archaic. In cartography, it is also a symbol for village: eight fields around a central square, and this is the source of its name. Octothorp means eight fields."

Robert Bringhurst, The Elements of Typographic Style; 2nd edition;
Hartley & Marks, Publishers, Point Roberts, WA; Vancouver, BC, Canada;
1996, p. 282.

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.

As seen in Wikipedia.