What is mechinical advantage

the advantage gained by the use of a mechanism in transmitting force

specifically : the ratio of the force that performs the useful work of a machine to the force that is applied to the machine

Mechanical is the ratio of the output and input forces.

For example, if a lever is balanced in the middle, then pushing on one end will yield the same amount of force on the other end. So the mechanical advantage is 1.

If instead that lever is balanced so that one side is twice as long as the other, then pushing on the long end will yield twice the force on the short end. The mechanical advantage would be 2.