Web Hosting Glossary

Bandwidth
This is how much network traffic (size of data being transported from host server to client browser) your site allowed to serve your visitors in specified time period (usually per month. Some server also restrict a daily bandwidth limit).
1 MB = 1024 kb. 1 Gb = 1024 Mb.
In average, an ordinary page with images would consume about 250 kb per view, depends on how much image and text in the page. So if you expect 1000 visitors a month who browse ten pages on each visit, you'll need about 2.5 Gb bandwidth. Just do the math with this simple formula:
reguired_monthly_bandwidth = expected_visitors x 2.5 Mb.
If a provider claims to offer "unlimited" traffic, be careful. Most likely they would not allow even more than 10 GB per month... Some provider will get outweighted by bandwidth consumed and look for "reason" to shutdown your site. So be careful, look-up for posts in their support forum from other clients.

Disk Space
This is how much space you are allowed to use to host your web files.
1 MB = 1024 kb. 1 Gb = 1024 Mb. If a provider claims to offer "unlimited" space, be careful. If it's true, the server will be extremely slow. Regardless of term "unlimited" means no limit, most likely they would not allow even more than 999 MB...
For a normal personal homepage you would not need more than 5 MB. An ordinary business web with hundreds of products/services would not need more than 100 Mb. If you have many sound files and large images, you might need more space.
Some providers might be able to offer you more space than what you initially received, if your site is very popular and you really need the extra space. Some other provider get weighted by space consumed and look for "reason" to shutdown your site. So be careful, look-up for posts in their support forum from other clients.

CGI-scripts
CGI (Common Gateway Interface) is special script that executed on server side to perform various tasks such accessing database, file operation, image generation, etc that can not be executed by common HTML operation. CGI add functionalities to your website. CGI can be written in any language supported by server operating system. Common language used in Linux-based server is PERL. Usually you can use pre-installed scripts provided by the free webspace provider (i.e., counter, guestbook, mail sender, etc.)
If you don't know what a CGI-BIN is, you most likely wont need it. CGI-BIN is place where you can put your own CGI scripts. Most free web hosts do not offer CGI-BIN for you to upload your own scripts due security reasons. If a free host do allow this, make sure your scripts don't take up too much system resources or they might remove your account. Most common examples of CGI scripts that many free hosts do not allow for this reason are banner exchange scripts and automatic-web-crawler scripts.