underbar

Underbar, commonly called the underscore, is the character represented by the symbol "_" in ASCII and Unicode. The term underbar appears in some technical writings as an alternative name for the same character, reflecting its traditional role as a substitute for underlining in plain text.

Historically, the underscore arose with typewriters and computer keyboards to provide a low, continuous line in situations where underlining was impractical. It remains widely used in digital contexts where spaces are not allowed, such as programming identifiers, file names, and URLs.

In programming and computing, underscores serve several purposes. They separate words in identifiers (snake_case) and may appear as leading or trailing characters to convey conventions (for example, a leading underscore to signal a private or protected member in some languages). In languages like Python, underscores are allowed in identifiers, with special meanings for leading or double leading underscores in certain naming schemes.

In text formatting, the underscore is often used as a substitute for underlining in plain text or to indicate emphasis in some lightweight markup systems, though many systems rely on asterisks or other conventions. In file systems and URLs, underscores help avoid spaces and improve readability.

The underscore is produced on keyboards by a dedicated key, and its code points include ASCII 95 and Unicode U+005F. It remains a versatile tool in both human-readable text and programming environments. See also: underscore character, snake_case, CamelCase.