Inertial sensors are sensors that detect and measure acceleration, tilt, impact, vibration, rotation and multi degree of freedom (DOF) motion.           
Inertial sensors include accelerometers (or accelerometers) and angular velocity sensors (gyroscopes), as well as their single axis, dual axis, and three-axis integrated IMU (inertial measurement unit), AHRS (attitude reference system including magnetic sensors).           
MEMS accelerometer is a kind of sensor which uses inertial force of sensing mass to measure. It is usually composed of standard mass block (sensor element) and detection circuit.           
The IMU is mainly composed of three MEMS acceleration sensors and three gyroscopes and calculation circuits.