Variation Selectors (Unicode block)
Variation Selectors is a Unicode block containing 16 variation selectors used to specify a glyph variant for a preceding character. They are currently used to specify standardized variation sequences for mathematical symbols, emoji symbols, 'Phags-pa letters, and CJK unified ideographs corresponding to CJK compatibility ideographs.
Source: Wikipedia — Variation Selectors (Unicode block) (CC BY-SA 4.0)