This character is a Other Symbol and is commonly used, that is, in no specific script.
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. U+2618 offers a line break opportunity at its position, except in some numeric contexts.
The CLDR project calls this character “shamrock” for use in screen reading software. It assigns these additional labels, e.g. for search in emoji pickers: irish, plant.
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 shamrock is a type of clover, used as a symbol of Ireland. Saint Patrick, one of Ireland's patron saints, is said to have used it as a metaphor for the Christian Holy Trinity. The name shamrock comes from Irish seamróg ([ˈʃamˠɾˠoːɡ]), which is the diminutive of the Irish word seamair and simply means "young clover".
At most times, Shamrock refers to either the species Trifolium dubium (lesser/yellow clover, Irish: seamair bhuí) or Trifolium repens (white clover, Irish: seamair bhán). However, other three-leaved plants—such as Medicago lupulina, Trifolium pratense, and Oxalis acetosella—are sometimes called shamrocks. The shamrock was traditionally used for its medicinal properties, and was a popular motif in Victorian times.