An encryption key is a string of characters used in cryptography to lock (encrypt) and unlock (decrypt) digital information. It acts like a password or code that ensures only authorized parties can access the protected data. Encryption keys are essential for securing sensitive communications, personal information, and online transactions. Without the correct key, encrypted data remains unreadable and safe from unauthorized access. Keys can be symmetric (the same key for encryption and decryption) or asymmetric (a pair of public and private keys).