Shared web servers are unique because they are split up into partitions that are assigned to each hosting account. A server partition is a section of a web server that is completely separate from the rest of the web server. Even though the partitions are completely separate, the server software configuration is the same across the entire web server. Server resources are distributed evenly amongst the server in the event of a partition overload. For example, if your web site is stressing the network's resources and pushing its limitations, then another server partition may aid in the operation of your web sites by providing extra server resources.
If you are consistently overstepping the boundaries of your shared server partition then you will most likely be warned by the web hosting provider via email. Too much excessive use can result in suspension of service or a hosting upgrade. Many shared web hosting plans offer unlimited features, however there are very real limitations, especially when the server limitations are consistently overused.