The main difference between grass trimmers and brush cutters is the level of work they can perform.
Grass trimmers typically feature a cutting head of nylon line or plastic blades and are designed for trimming grass and light weeds.
Brush cutters are typically more powerful and are generally capable of cutting thicker weeds, dense vegetation and undergrowth. Instead of using trimmer line, brushcutters may use blades to help tackle the more demanding work.
Although these definitions are helpful, it's important to understand they're not universally shared. The term "brush cutter" is sometimes used to describe any machine that has a straight shaft, regardless of power of intended use.
Our advice when choosing which machine to buy is to first identify what kind of work you will be doing, as this will help you choose the right machine for you.