Being in operation means that something is functional or actively working. Its opposite term or antonym would be non-operational, inactive, or out of service. These terms are used to describe something that is not currently functioning or working as it should be. For instance, a computer that is turned off or not responding is considered non-operational. Similarly, a machine that is broken, damaged, or not functioning correctly is also non-operational. In many cases, the opposite of being in operation denotes a state of inactivity or incapability, indicating that the entity cannot perform its intended purpose until it is fixed, replaced or reactivated.