Perpetual motion machine runs continuously and for infinite time. It never stops its motion and movement.
For a perpetual motion, there is no damping, friction and loss of energy. So the conservation of energy, momentum, mass principles enable the motion to continue indefinitely.
Such a motion may be periodic, or not, uniform or not..
For example the motion of Earth around Sun, and motion of Moon around Earth seem to be perpetual to the imagination of our known facts. Provided no external objects from outer space come and change the situation.