Final answer:
In SolidWorks, the assembly approach where pre-modeled parts are assembled is called Bottom-up assembly, which contrasts with Top-down assembly that starts with an overall layout.
Step-by-step explanation:
The assembly approach in SolidWorks where all the parts are already modeled and are then assembled together is called Bottom-up assembly. This approach involves the creation of individual parts separately followed by assembling them into a complete product. This is in contrast to the Top-down assembly, where the design begins with creating a layout of the entire assembly and then the individual parts are defined and designed within the context of that layout.