Plain meaning
Start with the shortest useful explanation before going deeper.
The process of converting plaintext data into ciphertext that can only be read with the correct decryption key. Symmetric encryption (AES) uses one key for both operations. Asymmetric encryption (RSA, ECIES) uses public/private key pairs. On Solana, encryption is used in confidential transfers (Twisted ElGamal), off-chain communication, and wallet security.