What is "octothorpe"

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. (context chiefly US English) The hash or square symbol ((unsupported: #)), used mainly in telephony and computing