A hash code is a numerical value generated from data using a specific algorithm. It serves as a unique identifier for that data, allowing for quick comparisons and retrieval. Hash codes are commonly used in computer science for tasks like data storage, retrieval, and integrity verification. When data is processed, even a small change will produce a significantly different hash code. This property makes hash codes useful in applications such as cryptography, data structures, and database indexing. They help ensure data consistency and security by allowing systems to detect alterations or duplicates efficiently.