Wireframes and Mockups both important for web design process.Both have some similarity and uniqueness.
This is very common terms you may have heard and as web designer you must had known to this. There are others two words which is similar to Wireframes and Mockups which is often used sketch and prototype.
All these four term sketch, wireframe, mockup and prototype are the process of designing an app and they look like this below images.
When ever you design or build app first step you do is rough sketch , just writing down all feature on blank page of paper.This is called sketch.
Second step you add organise the content and app elements is certain logical order like grouping similar element in one screen, and other element in other screen according to flow and requirement of application. This is called wireframe.
Third step you will do like add colours, icons type, pictures logos. It means you are going close to final step of designing to your wireframe. This is called mockup.
The last and final step is prototype means adding interaction with you mockup