const

Const is a keyword used in many programming languages to express immutability or to denote constant values. Its exact meaning and scope vary by language.

In C and C++, const qualifies an object or the value pointed to as read-only through a given pointer or reference. It can apply to data types and can be combined with pointers to create distinctions such as top-level const and pointer-level const (for example, const int x = 5; int* const p; const int* p;). Attempting to modify a const-qualified object yields a compile-time error; const-correctness helps enforce interfaces and can enable certain optimizations.

In JavaScript (ES6 and later), const declares a block-scoped binding that cannot be reassigned. The binding’s identity is fixed, but if it references an object or array, the contents of that object may still be mutated.

In Rust, const defines a compile-time constant. It must be initialized with a constant expression and is inlined wherever used. const is not mutable and has no run-time storage, unlike static items.

In C# and similar languages, const defines a compile-time constant value; it is implicitly static and must be of a primitive type or a string literal. For values that must be determined at run time, other constructs such as readonly are used.

Overall, const conveys immutability or fixed values, but the exact semantics depend on the language and context. Correct usage supports safety, clarity, and potential optimizations.