U+21D5 "⇕" Up down Double Arrow Unicode Character

U+21D5 "⇕" Up down Double Arrow is a typographic symbol that represents bidirectional movement or opposition in both vertical directions simultaneously, formed by two parallel horizontal lines with arrowheads pointing upward and downward. It is commonly used in mathematics, logic, and technical diagrams to denote a double-headed vertical relationship, such as logical equivalence when oriented vertically, or to indicate that a value or entity can move or apply both upward and downward. In computing and user interface design, this arrow may also signify a toggle or a bidirectional scroll or zoom function along the vertical axis, distinguished from its single-line counterpart by its double stroke, which suggests a stronger or more formal connection.