No, they are two different things. OCL, the Object Contraint Language, is used to describe constraints in a formalized language with C-like syntax. OCL has the same parents like UML, namely OMG. You find a desciption of OCL at OMG's site. UML can use OCL to describe constraints. So OCL is an extension to UML.
OCL is (my point of view) more an academic thing. You get along with textual constraints in almost all cases. Reading OCL isn't that difficult. Though writing a constraints in correct syntax takes time to learn. Being able to apply correct OCL will help machines to generate code from UML. Only a few tools can do that (honestly, I never used any of them).