Approximation algorithms are a type of algorithm that provide an efficient solution to optimization problems that may not have an exact solution within a reasonable amount of time. Instead of finding the exact optimal solution, approximation algorithms sacrifice accuracy for efficiency by finding a solution that is close to the optimal within a certain factor or ratio. These algorithms are widely used in various fields such as computer science, operations research, and mathematics to solve NP-hard problems where finding the exact optimal solution is not feasible. By providing solutions that are close to the optimal in a reasonable amount of time, approximation algorithms allow for practical and efficient problem-solving in complex situations.