The cache is also referred to as Temporary Internet Files.
Temporary Internet Files or cache are files like graphics, web pages, and cookies that are stored on your hard disk to speed up surfing. The idea is that if you surf to Amazon.com your browser will take certain files from that site and store them on your hard drive. The next time you surf to Amazon.com the page should load faster because you already have some of the information stored on your hard disk.
Does this mean you'll run out of space since it's storing and copying all these pictures and information to my hard disk? No, there's a limit to how much can be stored on the hard disk. Built in to Internet Explorer, Netscape and other browsers are areas where you can specify how much space you want to allow for storing Internet Files.
If you accidentally surf to sites that contain pornographic material for example, then all the pornographic pictures will be stored on your hard disk. Be careful. If your computer would happen to have adware or spyware software running on it, then others are going to know your surfing habits. Protect your privacy. Delete unwanted an unneeded files from your computer's hard disk.