Notebooks, netbooks and laptops use mobile processors. They are generally made to use less voltage, to spare battery life, and to run cooler because mobile machines don’t have huge fans and airy cases like desktops. As a general rule, the faster the CPU / GPU, the more heat it generates, so you will find cutting edge desktop CPUs are faster than cutting edge mobile processors, as it takes more money to make a CPU that is fast and runs cool, than one that can have a huge heatsync attached. Hence, desktop CPUs will always run ahead of mobile CPUs until/unless they find new technology.
With the advancement of mobile technology, laptops have evolved into what was previous considered a notebook, explaining why the terms have become interchangeable.