A recurrence relation is a mathematical equation that defines a sequence of numbers based on previous terms in that sequence. It expresses each term as a function of its predecessors, allowing for the generation of the entire sequence from a few initial values. For example, the Fibonacci sequence can be defined using a recurrence relation where each term is the sum of the two preceding terms. These relations are widely used in various fields, including computer science, to analyze algorithms and in mathematics for solving problems involving sequences. They help in understanding patterns and behaviors in sequences, making them a fundamental concept in both theoretical and applied mathematics.