M7 coprocessorA motion processor in the iPhone, starting with the iPhone 5S. Designed for tracking the user's movement, the M7 is a low-power processor that reads the output of the phone's accelerometer, gyroscope and compass and makes that data available to applications via Apple's CoreMotion programming interface (API). For example, it enables fitness apps and navigation apps to track movement for long periods of time without seriously draining the battery. See iPhone 5S.
For the iPhone 6, Apple's M8 coprocessor can determine if the user is running or biking. Its barometer can measure elevation, and it can track travel distance. See iPhone 6.