Number Sign

"#" or a number sign, is used in many ways. To see what it is used for, view "Uses"

Uses
Number Sign is used for social media, being called a "Hashtag" instead of a number sign. It is used for tags, which help a social media post or video be put on a category. It can also be used in phone numbers and to redact stuff, such as swear words or hidden credit cards.

Other Names
Hashtag is the only thing that is the number sign but has a different name.