A laptop, also called a notebook, is a personal computer for mobile use. A laptop integrates most of the typical componentsof a desktop computer, including a display, a keyboard, a pointing device (a touchpad, also known as a trackpad, and/or a pointing stick) and speakers into a single unit. A laptop is powered by mains electricity via an AC adapter, and can be used away from an outlet using a rechargeable battery.
Portable computers, originally monochrome CRT-based and developed into the modern laptops, and were originally considered to be a small niche market, mostly for specialized field applications such as the military, accountants and sales representatives. As portable computers became smaller, lighter, cheaper, more powerful and as screens became larger and of better quality, laptops became very widely used for all sorts of purposes.
From Wikipedia http://en.wikipedia.org/wiki/Laptop