Is one way valve a check valve? 

One way valve is one kind of valve where the fluid can only flow along the inlet, but the medium in the outlet couldn’t flow back. Sometimes, the one way valve is also called check valve. 

Actually, one way is one kind of check valve, both of them are used to prevent the back-flow of the medium, they both have the same function, they are used in various pipelines or devices to prevent the mediums from flowing back.