A trie, also known as a prefix tree, is a tree-like data structure used to store strings, where each node represents a single character of a string. Tries are commonly used in scenarios where quick retrieval of strings or prefixes is important, such as in autocomplete systems, spell-checking, or searching for words in a dictionary. The root of the trie represents the empty string, and each path from the root to a leaf node forms a valid word. Each node in a trie has a number of children equal to the possible characters (typically the alphabet for English words), and words are inserted by adding characters one at a time along the path from the root to a leaf. The key advantage of a trie is its ability to search for a word or prefix in O(k) time, where k is the length of the string, regardless of the number of strings stored in the trie. This makes it much faster than other data structures like hash tables or binary search trees when working with a large set of strings. Tries are also useful in algorithms like searching for substrings, implementing IP routing, and solving problems involving pattern matching or regular expressions.