Gyroscopes are devices that measure angular velocity, or the rate of change of an object's orientation. They're found in a variety of applications, from aircraft navigation systems to video game controllers. While some gyroscopes are powered by electricity, others use mechanical or optical means to detect movement.
There is no single answer to the question of whether or not a gyroscope is an app. It depends on how the term app is defined. If an app is simply a software application, then there are certainly apps that make use of gyroscopes (such as those mentioned above). However, if the definition of app is narrower and refers only to mobile apps, then there may not be any that specifically utilize gyroscopes (although there could be some that work with other sensors like accelerometers).