Coilovers vs Struts: What's the Difference? 

There are two general stock configurations of coil springs and shock absorbers. In some cars, the coil spring is located apart from the shock absorber, supporting the vehicle on its own. The shock is mounted separately from the spring.
In other configurations, the coil spring is mounted to the shock absorber as a single unit supporting the vehicle. This is typically referred to as a strut but is sometimes called a coilover. In fact, coilover is just a shortened version of “coil spring over shock absorber,” and sometimes coilovers are indeed struts but not always. In the field, the main difference between coilovers vs. struts is adjustability and customization.