What is a non verbal contract?

It is a contract that is not spoken and is not written down.

For instance, an implied contract would be a non-verbal one.

Read the following links for more information on non-verbal contracts:
Implied in fact contract - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Implied_in_fact_contract)
Quasi-contract - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Implied_in_law_contract)