Symmetric message authentication code key

Definition
in a symmetric message authentication code (MAC) key,

"A symmetric key is used to provide assurance for the integrity of data. There are three techniques used to provide this assurance: 1) use a symmetric encryption algorithm and a MAC mode of operation (e.g., CMAC using AES); 2) use a symmetric encryption algorithm and an authenticated encryption mode of operation (e.g., GCM or CCM using AES); and 3) use a hash-based MAC (HMAC). For data-in-transit, a symmetric MAC key has a short life, typically for a single message or for a single session (for example a TLS session). For stored data, the life of a symmetric MAC key tends to be for as long as the data needs to be protected."

Overview
"Note that when authenticated encryption mode is used, the same key is used for both the MAC and encryption/decryption, since both objectives are achieved by invoking a single mode of operation."