OEM

Original Equipment Manufacturer. The company that originally made the hardware that is in use, whether a sound card or a complete system. OEM versions of software are usually the same as software found in shops but without the packaging.

Offline

A computer is offline when it is not connected to a remote server. For example, if a modem is not using a phone line then it is offline.

Online

Exactly the opposite of Offline - if a computer is connected to a remote server, then it is online. For example, if a modem is using a phone line, then it is online.

OS

Operating System. The software that controls the actual operation of the PC, including the way that the software controls the hardware of the PC.