Hash (#), or hash, is a special character on the keyboard that is used for special tasks in HypertextMarkup Language( HTML), among other things.
The hash character is used, for example, to mark permalinks and on Twitter to convolute words and the associated listing of thematically related tweets.
The hash character has the decimal number 35 in the ASCII character set, hexadecimal 23 and is on common QWERTY keyboards. The hash character is also used as a tag in tweets from Twitter, marking words or parts of sentences in Twitter tweets. These marking characters are called hashtags: Tags based on hashes.