A VAR is a Value Added Reseller which in this case is someone who sells space on servers that do not belong them. A VAR might offer some other service which make them an attractive choice, such as support in a particular language or knowledge of a certain industry. Exactly how much control a particular VAR has over the servers they sell space on will vary widely. The provider will not charge you extra if your web site receives lots of visitors. The more visitors you receive, the more data is transferred from the server, and the more bandwidth this uses.
Some providers charge for high bandwidth usage to prevent their servers from being overloaded.
Although many people prefer not to be charged in this way, it may be in your best interests, since it gives some assurance that the server which you will be sharing with several other web sites will not become hopelessly overloaded. Furthermore, most providers allow a certain amount of bandwidth before charges apply, and this minimum level is often much higher than your site is going to generate even in your busiest months. An image which has multiple hot spots on it which link to different pages. For example, it might be a picture of several people setup so that clicking on a persons face takes you to a web page about that person. Image maps can be done on the server or on the client, and each has its pros and cons.