An algorithm is a step-by-step procedure or formula for solving a problem or completing a task. It consists of a sequence of instructions that can be followed to achieve a specific outcome, often used in computer programming and mathematics. Algorithms can vary in complexity, from simple calculations to intricate processes that manage large data sets. In computer science, algorithms are essential for tasks such as sorting data, searching for information, and performing calculations. They are evaluated based on efficiency and effectiveness, often measured in terms of time complexity and space complexity. Common examples include sorting algorithms like QuickSort and search algorithms like binary search.