In present day…
The # has been used in social media and referred to as a hashtag. The idea of calling it “hash” came out in the 1970s. It has also been referred to as the pound sign and the number sign. It had been called the pound sign because when scribes wrote it “lb”, a line was often slashed across the top of the “lb” creating a similar appearance to the “#” symbol. However, not to confused with the British form of currency, they would refer to it as the number sign, such as in a number two pencil (#2). Other names for the symbol include “tic-tac-toe,” “crunch,” “square,” etc.
Octothorpe was actually a made up word.
It was formulated by technicians when creating the “*” and “#” symbols on the phone in the 1960s. It had many spelling deviations: octothorp, octotherp, octatherp, etc. One of the theories of why they chose that name was that it had the appearance of a town surrounded by eight fields, “octo” meaning eight and “thorpe” meaning fields. Another theory was that it was named after an athlete, Jim Thorpe.