The Open Web is what librarians call information that is freely available on the Internet. In some classes your professors may ask you not to use information from the Web. However for some subjects, especially those that change the most quickly, the Web may hold very important resources. It's important to remember that while the Internet is an excellent tool for distributing large amounts of information quickly it is not centrally organized or controlled in any way.
This means that you need to be careful to distinguish good information from bad, and that a quick search engine search may not find everything that you want. However, a search engine can be a very useful tool.