They see a perpertual machine as one that does useful work. But it does not draw on an external force. Here is another way of saying this. It is a machine in which the output is greater than the input. This ultimately leads to a machine that can create energy.
Perpertual motion has a history.
According to this history, perpetual motion arose in connection with the search for a machine or mechanism. This mechanism would continue to do useful work once it was set in motion. Or it would give more energy than it absorbed in a cycle of operation. There were some early perpetual motionists. They saw perpetual motion on a large scale every day.