An active system is defined as a system that is always in motion or functioning. There are several synonyms that can be used to describe an active system, such as dynamic, live, bustling, kinetic, and vigorous. A dynamic system is always changing and evolving, while a live system is full of energy and excitement. A bustling system is busy and active with people or activity, and a kinetic system is constantly moving and in motion. A vigorous system is powerful and able to sustain a high level of activity or exertion. No matter which synonym is used, all describe the characteristics of an active system, and all convey the idea of something that is always moving and functioning.