The # symbol is officially called an octothorpe
The symbol # is officially named the 'octothorpe'. The 'octo' refers to its eight points. The 'thorpe' is disputed — possibly after an obscure word for 'village', possibly after a joke by engineers at Bell Laboratories in the 1960s who named it after Jim Thorpe (the athlete) while working on telephone keypads. It has also been called a 'pound sign' (from the abbreviation for pounds weight, Lb), a 'number sign', a 'hash', and a 'sharp' in music notation. Twitter's use in 2007 transformed it into the 'hashtag'.
A symbol seen billions of times per day as a hashtag has a strange and disputed proper name. The gap between how universal the symbol is and how unknown its official name remains is a quiet measure of how much language floats free of its labels.
“The # symbol is officially called an octothorpe. The name may have been invented as a joke by Bell Labs engineers in the 1960s. Before Twitter, most people called it a pound sign. #OddlyHuman”