The cryptographic transformation of data to produce ciphertext.
Sources:
CNSSI 4009-2015 from ISO/IEC 7498-2
NIST SP 1800-21B under Encryption from CNSSI 4009-2015
NIST SP 800-12 Rev. 1 under Encryption from ISO 7498-2

  Cryptographic transformation of data (called “plaintext”) into a form (called “ciphertext”) that conceals the data’s original meaning to prevent it from being known or used. If the transformation is reversible, the corresponding reversal process is called “decryption,” which is a transformation that restores encrypted data to its original state.
Sources:
NIST SP 800-82r3 under Encryption from RFC 4949 - adapted

  Any procedure used in cryptography to convert plain text into cipher text to prevent anyone but the intended recipient from reading that data.
Sources:
NIST SP 800-101 Rev. 1 under Encryption
NIST SP 800-72 under Encryption

  The process of changing plaintext into ciphertext using a cryptographic algorithm and key.
Sources:
NIST SP 800-133 Rev. 2 under Encryption
NIST SP 800-57 Part 1 Rev. 5 under Encryption
NIST SP 800-57 Part 2 Rev.1 under Encryption

  The process of transforming plaintext into ciphertext.
Sources:
NIST SP 800-20 under Encryption
NIST SP 800-67 Rev. 2 under Encryption

  The process of a confidentiality mode that transforms usable data into an unreadable form.
Sources:
NIST SP 800-38A under Encryption (Enciphering)

  The process of transforming plaintext into ciphertext using a cryptographic algorithm and key.
Sources:
NIST SP 800-56B Rev. 2 under Encryption

  The process of changing plaintext into ciphertext using a cryptographic algorithm for the purpose of security or privacy.
Sources:
NIST SP 800-175B Rev. 1 under Encryption

  The process of changing plaintext into ciphertext.
Sources:
NISTIR 7621 Rev. 1 under Encryption from CNSSI 4009-2015, ISO/IEC 7498-2