Big Omega is a notation used in computer science to describe the lower bound of an algorithm's running time. It provides a guarantee that the algorithm will take at least a certain amount of time to complete, regardless of the input size. This helps in understanding the efficiency of algorithms, especially in the worst-case scenario. In mathematical terms, if a function f(n) is said to be in Ω(g(n)), it means that there exist positive constants c and n₀ such that for all n greater than or equal to n₀, f(n) ≥ c * g(n). This notation is essential for analyzing algorithms and comparing their performance.