Octothorpe, it's a real word Dammit:

I occasionally drop my "Everybody hates math know-it-alls" defense and use the word Octothorpe. It never fails that someone challenges it as a made up word, so I'm just posting this so that when they ask I can reference a source.... Ok, I'm not unknowing of the circular reference, but hey, they are normally too dumb to think of that, so here goes:

Octothorpe: In the 1960's when Bell Telephone added two new buttons for push button telephones, they used the * symbol and the # symbol. Although most people call the * an asterisk, the telephone folks decided to use "star". other symbol, #, has been called lots of different names such as crosshatch, tic-tac-toe, the pound sign, and the number sign (leave it to the telephone company to put the number sign on one of the two keys without a number); but the term now used by the American telephone industry for the symbol is octothorpe although it is more often called the pound key in conversations with the public. It seems that the name was made up more or less spontaneously by Bell Engineer Don MacPherson while meeting with their first potential customer. The octo part was chosen because of the eight points at the ends of the line segments, and the thorpe was in honor of Jim Thorpe, the great Native American athelete. Why honor Thorpe? At the time MacPherson was working with a group that was trying to restore Thorpe's olympic medals, which had been taken from him when it was found he had played semi-professional baseball prior to his track victories in the Olympics in Sweden. [It's not math, but I love the story that when the King of Sweden gave him the gold medal, the king said, "You are surely the greatest athlete on the earth". The modest Thorpe smiled and replied, "Thanks, King."]
There are a host of other names for the # symbol, and many of them can be found at this page from Wikipedia which includes several different stories about the creation of "octothorpe" or "octothorn" and also has this rather interesting clip:
"The pronunciation of # as `pound' is common in the US but a bad idea. The British Commonwealth has its own, rather more apposite, use of `pound sign. On British keyboards the UK pound currency symbol often replaces #, with # being elsewhere on the keyboard. The US usage derives from an old-fashioned commercial practice of using a # suffix to tag pound weights on bills of lading. The character is usually pronounced `hash' outside the US. There are more culture wars over the correct pronunciation of this character than any other, which has led to the ha ha only serious suggestion that it be pronounced `shibboleth' (see Judges 12:6 in an Old Testament or Tanakh)." The page also disputes the use of "square" in Britain.

Origqinally posted on my now obsolete Math Words and Other Words blog.