when a force is applied on a body for example a door, it rotates around a fixed point called axis of rotation or pivot.
suppose we exerts force on the outer edge of the door. in this case the perpendicular distance between the pivot and the point where we exerts force is called moment arm or moment. it is denoted by r
as u can see in torque's equation
T = r * F
this r is moment. this is a distance measured in meters.