Explanation:

An algorithm is a finite sequence of well-defined, unambiguous, and computer-implementable instructions, typically designed to solve a specific class of problems or perform a computation. It is a step-by-step procedure for solving a problem, especially by a computer. Option (d) An algorithm perfectly matches this definition. Option (a) A compiler is a program that translates source code. Option (b) A code is a general term for program instructions, but less precise than 'algorithm' for a 'prescribed set of instructions'. Option (c) A description is merely an account of something, not the set of instructions itself.