This character is a Other Symbol and is commonly used, that is, in no specific script. The character is also known as poison.
The glyph is not a composition. It has no designated width in East Asian texts. In bidirectional text it acts as Other Neutral. When changing direction it is not mirrored. The word that U+2620 forms with similar adjacent characters prevents a line break inside it.
The CLDR project calls this character “skull and crossbones” for use in screen reading software. It assigns these additional labels, e.g. for search in emoji pickers: bone, crossbones, dead, death, face, monster, skull.
This character is designated as an emoji. It will be rendered as monochrome character on conforming platforms. To enable colorful emoji display, you can combine it with Variation Selector-16: ☠️ See the Emojipedia for more details on this character’s emoji properties.
The Wikipedia has the following information about this codepoint:
A skull and crossbones is a symbol consisting of a human skull and two long bones crossed together under or behind the skull. The design originated in the Late Middle Ages as a symbol of death and especially as a memento mori on tombstones.
In modern contexts, it is generally used as a hazard symbol, usually in regard to poisonous substances, such as deadly chemicals.
It is also associated with piracy and software piracy, due to its historical use in some Jolly Roger flags.