• The plaintext is the original message.
• The ciphertext is traditionally a message that has been transformed to provide confidentiality.
• A cipher is a cryptographic transformation that is used to encrypt or decrypt a message.
• A message authentication code (or MAC) is a piece of data that provides authenticity and integrity. A MAC algorithm is used both to generate and validate this code.
• To encrypt a message is to apply a confidentiality transformation, but is often used to describe a transformation that satisfies all three goals.
• To decrypt a message to reverse the confidentiality transformation, and often indicates that the other two properties have been verified.
• A hash or digest algorithm transforms some arbitrary message into a fixed-size output, also called a digest or hash. A cryptographic hash is such an algorithm that satisfies some specific security goals.
• A peer or party describes an entity involved in the communication process. It might be a person or another machine.
• ciphersuite: a selection of algorithms that we’ll use to provide security.
• nonce: a nonce is an arbitrary number that can be used just once in a cryptographic communication. It is often a random or pseudo-random number issued in an authentication protocol to ensure that old communications cannot be reused in replay attacks. They can also be useful as initialization vectors and in cryptographic hash functions.

References

• https://leanpub.com/gocrypto/read#leanpub-auto-chapter-1-introduction

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