An Actual machine is that in which there is a loss of energy in some manner. In an actual machine, the work output is less than the work input, i.e., efficiency of an actual machine is always less than 100%.

In Actual machines, mechanical advantage is less than velocity ratio.

An ideal machine is that in which there is no dissipation of energy in any manner. In an ideal machine, the work output is equal to the work input, i.e., efficiency of an ideal machine is 100%.
In ideal machines mechanical advantage is equal to velocity ratio.