An output arm is the end of a lever that moves the load up when force is applied to the other end of the lever. The upward force that moves the output arm is the output force.
A lever is a stiff structure that rotates on a fixed point. This fixed point is the fulcrum. The side of the lever that receives force is the input arm. The input force is what moves the input arm down and causes the output arm to move upward, raising the load. Levers are highly versatile because the fixed point, or fulcrum, can be moved and arranged to adapt to the task.
There are three classes of levers: first-class, second-class and third-class levers. First-class levers always have a fulcrum between the input force and the output force. Second-class levers have the output force between the fulcrum and the input force. Third-class levers always have the input force between the fulcrum and output force.
A real-world example of a lever with an output arm is a typical playground seesaw. The side that rises as a result of someone sitting on the other side is the output arm. A seesaw is a first-class lever because the fulcrum lies between the input and output forces.