Generally speaking, the back office refers to the activities of a company that are not in direct interaction with the customer (e.g. administrative, logistical, etc.), as opposed to the front office. In IT, the frontend refers to the part of an application or site that is visible to the end user, the backend being the part not visible to the user and managed by the developers and/or operators of the application or site.[1]
[1] https://aws.amazon.com/fr/compare/the-difference-between-frontend-and-backend/