What is Encryption?
Transforming readable data into ciphertext with a key, so only parties holding the right key can recover the original.
Definition
Encryption converts plaintext into ciphertext that is useless without the decryption key. Symmetric algorithms like AES-256-GCM use one shared key and are fast enough for bulk data; asymmetric schemes like RSA and elliptic-curve cryptography use a public/private key pair, solving key distribution and enabling digital signatures. TLS combines both: an ECDHE key exchange establishes a session key, then symmetric ciphers protect the traffic. Data should be encrypted in transit (TLS) and at rest (disk or database-level encryption, with keys held in a KMS or HSM). Never invent your own cipher — use vetted libraries like libsodium.