A computer process where the main constraint to improved performance is the speed of the CPU in the machine. For example, calculating Pi is usually a CPU bound process. If you put in a processor (of the same type) that's twice as fast, you'll get close to twice the speed of calculations.

Another example of a CPU bound process is ray tracing. There is some I/O (reading the scene description and writing the output image), but it's mostly calculations. Hence upgrading your processor would improve ray tracing speed. But, say, buying a faster hard disk would not.

It's important to work out whether your process is CPU bound or I/O bound when you're trying to improve system performance.

The opposite of CPU bound process is an I/O bound process.