Answer
Acceleration
Acceleration Means rate of Change of velocity with respect to time.
acceleration due to gravity
when a body falls freely means no other force act on it except gravitational force that time velocity of object does not remains constant but it changes as it approaches towards the ground it means body get accelerated and this acceleration which is gained by the body due to gravitational force is called its acceleration due to gravity it is denoted by g. Acceleration due to gravity is different on different planet. SI unit of is m/s^2 . On earth its standard value is 9.80665m/s^2.