PMEVC stands for Product Modeling Environment for Variant Configuration, i.e. it is a modeling tool for your product configuration model and its objects related to Variant Configuration. You can find more information on the help page, see for example here:
One of the biggest advantages of using PMEVC that you can view the product configuration model as a whole, can maintain its configuration objects and even have the possibility to test the model.
If you would like to learn more about Variant Configuration and the relevant SAP solutions, you can refer to the SAP help pages, respectively. (This depends hugely on the solutions you or your company are interested in.)
If you want to get involved in the Variant Configuration community, you can check out the SAP Configuration Workgroup. There also exist a book about 'Variant Configuration with SAP' published by SAP Press.