@wikipedia

Synonym: Closed-form expression = Explicit expression

A mathematical expression expressed using a finite number of basic arithmetic operations over the numbers and elementary functions.

The key benefit of dealing with closed-form expressions is that they are

• well tabulated with precision enough for the majority of engineering applications
• implemented as fast-computable algorithms with computer precisions (usually 64 bit and 128 bit) on modern  computers
• available as fast-computing algorithms with arbitrary user-defined precision

See also

Formal science / Mathematics / Calculus / Mathematical expression

[ Quadrature ][ Implicit expression ][ Analytic expression ][  Closed-form expression ]