This article will define what various terms used by web hosting companies mean. It's not possible (and sometimes insulting to the reader) to cover everything so this will just cover the most commonly used and important terms.
Bandwidth (or Transfer or Data Transfer)
Bandwidth is the amount of traffic that is sent (and recieved) by your website. It is usually measured in gigabytes (GB), where 1 GB = 1024 megabytes (MB), and it is usually allocated on a monthly basis, for example you could have 5GB/month of bandwidth, which means that there is a limit of 5GB of files that can be downloaded from your site within a month. Bandwidth is only a concern if you host a lot of files, for example images or movies, as webpages are usually small file sizes.
Colocation Server (or Colocation Hosting)
This is similar to Dedicated Hosting (see below), except the server is owned by a customer and they pay the colocation hosting company to host the server for them - that involves paying a charge for bandwitch which the hosting company provide, the physical space which the server takes up and the power that the server uses. With this set up the customer is responsible for their hardware.
This is a web page with a usable interface which the customer can connect to when they want to tweak their hosting settings, view the transfer statistics, or utilise other features provided with their hosting.
Dedicated Server (or Dedicated Hosting)
This is a server which is owned by the hosting company which they will rent out to you for a monthly fee along with an allotment of bandwidth which you can use with it. This means that you get a whole server to yourself to use for what you desire, this is needed for scripts which use a lot of server resources (for example large message boards, for one of which I pay for a dedicated server). As a customer, you would have full control over the server and could change the configuration as required, a facility not available when you have to share a server with others. With a dedicated server, the web hosting company is responsible for the hardware as they own it, not the customer.
This is the amount of space on the server that you have to upload your files on, it's usually measured in MB or GB.
This is a type of database (as is PostgreSQL) which allows the customer to store and retrieve information on the server. A lot of scripts require that a database is present to function.
This is similar to Virtual Hosting (see below), but the customer is given the ability to create small hosting accounts of their own, which they can then give or sell to people if they desire. It usually allows the customer more features, bandwidth and diskspace than with normal virtual hosting.
Scripts (eg PHP, Perl, ASP)
These are server side scripting languages which allow the customer to use already written scripts, or write their own, which provide additional features for the website and increased interactivity (for example message boards and content management systems).
Virtual Hosting (or Shared Hosting)
This is where a webhosting company puts many customers' webpages on the same server - so the server resources are shared amongst all the customers using it. This means that applications which cause a high server load are not suitable, and if one customer uses one then other customers will suffer.