Also known as engine clock, GPU clock speed indicates how fast the cores of a graphics processing unit (GPU) are. The function of these cores is to render graphics; therefore, the higher the GPU clock speed, the faster the processing.
The engine clock is measured in megahertz (MHz), with one MHz being equal to one million hertz. As is the case with total clock speed for a CPU’s computing tasks, the GPU clock speed translates into how many processing cycles per second can be executed by the graphics processing unit.
Although the engine clock is not the only element to impact a GPU's performance, a fast GPU is particularly valued by gamers, image editors, and other people who deal with image processing tasks. To obtain increased performance, some users opt for overclocking, a process that consists of running the GPU (or a CPU) faster than the speed established by the manufacturer.
GPU clock speed is one of the most relevant specs to watch for when choosing a graphics card for your computer, especially if you're into gaming or other graphics-intensive activities.