The fundamental purpose of an algorithm in computer science is to provide a precise set of instructions for solving a specific problem or performing a task. Algorithms are essentially step-by-step procedures that outline how data is to be processed or manipulated. They can range from simple functions, like sorting or searching, to complex calculations in machine learning. By defining clear algorithms, programmers can ensure that their code efficiently solves problems and achieves desired outcomes, making them foundational to software development and computational tasks.