What is "number sign"

octothorp \oc"to*thorp\, octothorpe \oc"to*thorpe\, n. [octo- eight + thorp Etymology of thorp uncertain. (ca. 1965). See quote below. Possibly derived from octalthorpe or octotherp (once used by the Bell System?).] 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 (meaning: number thirty-six).

octothorp 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 (2d edition, 1996), Hartley & Marks, Publishers, Point Roberts, WA; Vancouver, BC, Canada, p. 282)

n. The character (unsupported: #) used to represent the word ''number''; the hash sign; also called the pound sign in the US

The symbol # is most commonly known as a number sign, hash, or pound sign. Other names include octothorpe and hashtag. The symbol is used for a variety of purposes, including the designation of a number (for example, "#1" represents "number one"), an abbreviation for pounds avoirdupois in the food industry, a searchable metadata tag on social media platforms, and a button on telephone keypads. The symbol is defined in Unicode as .

The symbol may be confused with the musical symbol called sharp . In both symbols, there are two pairs of parallel lines. The main difference is that the number sign has two horizontal strokes while the sharp sign has two slanted parallel lines which must rise from left to right, in order to avoid being obscured by the horizontal musical staff lines.