Prefix sums are a powerful technique in competitive programming for efficiently answering range queries on an array. The idea is to precompute an array where each element at index i represents the sum of the elements from the start of the array up to i. Once the prefix sums are computed, you can quickly calculate the sum of any subarray by subtracting the prefix sum of the left boundary from the prefix sum of the right boundary. This reduces the time complexity of range sum queries from O(n) to O(1), making prefix sums ideal for problems involving multiple range queries.