An accelerometer is a device that measures the vibration, or acceleration of motion of a structure. The force caused by vibration or a change in motion (acceleration) causes the mass to "squeeze" the piezoelectric material which produces an electrical charge that is proportional to the force exerted upon it.
A Gyroscope can be understood as a device that is used to maintain a reference direction or provide stability in navigation, stabilizers, etc. Similarly, a gyroscope or a Gyro sensor is present in your smartphone to sense angular rotational velocity and acceleration.
Gyro sensors, also known as angular rate sensors or angular velocity sensors, are devices that sense angular velocity. In simple terms, angular velocity is the change in rotational angle per unit of time. Angular velocity is generally expressed in deg/s (degrees per second).