Service account
A non-human account used by an application or automated process to authenticate.
These are consistently the weakest accounts in an environment: passwords that never change because nobody knows what would break, privileges granted broadly to make something work years ago, and no MFA because a script cannot answer a prompt.
The improvements available are managed service accounts that rotate automatically, scoping rights to exactly what the process needs, and blocking interactive sign-in so the account cannot be used by a person.
Where this comes up
Service account sits inside our identity and access work. If you are trying to work out what this means for your own environment rather than in the abstract, that is the page worth reading next, and a short call will get you a straight answer faster than either.