OCR: Optical character recognition - When your computer gets a fax or scans in text, all it sees are graphical bits on a virtual page. That text is not usable, searchable, or editable. If you pass the page through an OCR program, the software converts the shapes on it into a text document. However, few documents are perfectly recognized and the errors are frequent if the type is small or the scan unclear. But the conversion is often faster than typing text manually.
OEM: Original equipment manufacturer - Originally OEM was an adjective used to describe a company that produced hardware to be marketed under another company's brand. Mitsumi, for example, produced CD-ROM drives that dozens of companies would label as their own. When purchasing OEM products you usually get a great price, but little to no warranty, manuals or pretty packaging.
Operating System: The most important program that runs on a computer. Every general purpose computer must have an operating system to run other programs. Operating systems perform basic tasks, such as recognizing input from the keyboard, sending output to the display screen, keeping track of files and directories on the disk, and controlling peripheral devices such as disk drives and printers. Examples include Windows XP and Linux.
Orb: Thermatake have adopted this name for a line of conical-finned heatsinks that are based loosely on a design used in HP servers in the 80's. The heatsinks have the fan located in the midst of the fins which allows the unit to offer a good price/performance ratio.
OSD: On Screen Display - How digital monitors can be configured.
Overclocking: Making a processor run at a higher then normal clock speed. For instance, changing the multiplier so that a 500Mhz chip runs at 667Mhz. This is a way to get more out of your chip then you paid for, but hardware failure is a risk.