One online definition of the word goes as "mechanical device consisting of a toothed wheel or rack engaged with a pawl that permits it to move in only one direction." More here.
The method goes like:
- What are the issues involved in your problem?
- Deal with the bigger issues first. Only after you have finished with a main issue, you go down to the next/lower level issue.
- And you mustn't come back up to the main issue over and over.