An encryption key is a string of characters used in cryptographic algorithms to encode or decode information. It acts as a secret component that converts plaintext into ciphertext, making data unreadable to unauthorized users. The strength of encryption largely depends on the complexity and length of the key. There are different types of keys, such as public keys used in asymmetric encryption and symmetrical keys used in symmetric encryption. The management of encryption keys is crucial for safeguarding sensitive information in various applications, including online transactions and secure communications.