decl

Decl, short for declaration, is a term used in programming and computer science to denote a statement that introduces an identifier and its attributes (such as type or signature) to a program’s scope. A declaration may or may not allocate storage and generally does not provide executable code; it tells the compiler or interpreter that a symbol exists and how it should be used.

In many languages, declarations establish interfaces separate from definitions. For example, in C or C++, the line extern int x; is a declaration of x, while int x = 5; both declares and defines x by providing storage and an initializer. Function prototypes like int add(int a, int b); declare the function’s name and signature without implementing it. Declarations are commonly placed in header files to separate interface from implementation.

Other contexts use the concept of declarations in type systems and interface definitions. In TypeScript and other languages with ambient declarations, the keyword declare marks a declaration that describes the shape of code defined elsewhere. In Interface Definition Languages, declarations specify interfaces, methods, and types that implementations must follow.

Decl is thus a general shorthand used in code comments, symbol tables, and documentation to refer to a declaration rather than a definition or implementation. The term is not a language itself but a linguistic tool for clarity in technical writing and tooling.

See also: declaration, definition, forward declaration, function prototype, ambient declaration.