1) In computers, the form factor is the size, configuration, or physical arrangement of a computing device. The term is commonly used in describing the size and/or arrangement of a device, acomputer case or chassis or one of its internal components such as a motherboard or a daughterboard. If you see the term applied to software or programming, it will usually mean the size of the program or the amount of memory required to run the program effectively. When used to refer to the size of a free-standing computer or other device, it's close in meaning to footprint.
Notebook computers, for example, are a form factor unto themselves because they all take the same "clamshell" form, are typically rectangular and open to a keyboard on the flat surface and a screen on the top. Notebooks are also available in a variety of form factors that identify a type of product and market area.
Here are a few different notebook form factors:
A netbook is a small, light, low-power notebook computer that has less processing power than a full-sized laptop but is still suitable for word processing, running a Web browser and connecting wirelessly to the Internet.
2) In electric motor terminology, a form factor is the amount of rectified current emitted from a direct current (DC) power source and is expressed as a ratio of the root-mean square (rms) value of the current to the average (av) current or Irms/lav. If the form factor differs much from pure non-pulsating DC (a value of 1.0), it indicates the possibility that motor and brush life will be shorter.