Disk space offered by a web host to put your website on. Just as each file on a computer takes up a certain amount of space, so to does a file on a web host take up space, thus the amount of web space your host provides determines how large of a website you can have. Unless you want a huge website that is going to have a lot of images, animations, software to download, or pages then you probably aren't going to need more than the 50 megs offered by most webhosts.