As used in this article:
"Contractor" means a person, his assigns or legal representatives, with whom a contract with a public agency is made.
"Public agency" means any county, city, town, township, public commission, public board or other municipality in this state authorized by law to make contracts for the making of any public improvement in any city, town, township or other municipality.
"Subcontractor" means a person having a contract under a contractor for the performance of the same work, or any specified part thereof, and also a person having such a contract with a subcontractor, for the performance of the same work or any specified part thereof.