Backup - A copy on floppy disk or tape of files on a PC's hard disk. A backup is used in case the hard disk file(s) are erased or damaged.
Bit, bytes - A bit is the smallest piece of information that computers use. For simplicity, a PC uses bits in groups of 8 called bytes (8 bits = 1 byte).
Boot, boot up, boot disk - You boot (or boot up) your computer when you switch it on and wait while it prepares itself. Instructions for startup are given to the computer from the boot disk, which is usually the hard disk.
Browser, to browse - A browser is a program like Netscape or Internet Explorer. You use it to view or browse the Internet.
CD-ROM - A disk for storing computer information. It looks like an audio CD.
CPU - Central Processing Unit. This is a PC's heart or 'brains'