A Feistel Network is a symmetric structure used in block ciphers for encryption and decryption. It divides the input data into two halves and processes them through multiple rounds of transformation. Each round applies a function to one half and combines it with the other half, allowing for complex encryption while maintaining the ability to reverse the process easily. This design is named after Horst Feistel, who introduced it in the 1970s. Many well-known encryption algorithms, such as DES (Data Encryption Standard) and Blowfish, utilize the Feistel Network structure, making it a fundamental concept in cryptography.