"Laptops" and "notebooks" are used interchangeably like "PC" and "computer". However, there are some tech neophytes who uses the term "CPU" instead of "computer" or "PC".
Laptops / notebooks generally fall into two major categories: portable (light enough to carry around) and desktop replacement (big and heavy). Desktop replacement laptops are usually more powerful than portable laptops.
"Ultrabooks" are relatively new. These are light, powerful enough laptops that generally have long battery life. These tend to be more expensive than your average portable laptop.
"Netbooks" have been around for sometime. They are small, light, inexpensive and not very powerful at all. They can be smaller and sometimes lighter than ultrabooks. Good enough for basic tasks, and not good enough to play games with.