Explanation:
Symmetric encryption is a cryptographic technique where the same key is used for both encrypting and decrypting data. This method is efficient and fast, making it suitable for large volumes of data.

The sender and receiver must securely share the same secret key to use symmetric encryption. Popular symmetric encryption algorithms include AES (Advanced Encryption Standard) and DES (Data Encryption Standard).

Due to its speed, symmetric encryption is commonly used for securing data in storage, encrypted communication, and file transfers. However, its primary challenge lies in secure key distribution.

Additional Information:
Symmetric encryption is often employed in combination with asymmetric encryption in hybrid cryptosystems, where asymmetric techniques secure key exchange while symmetric algorithms handle data encryption.

Key management and secure key exchange remain significant challenges. If the shared key is compromised, the confidentiality of the encrypted data is also compromised.

Formal Definition:
Symmetric encryption is a cryptographic method that uses the same key for both encrypting and decrypting data, ensuring confidentiality and secure communication.