As mentioned earlier, there are often several different ways of referring to the same thing (interest groups, special interests, lobbying). Because many of the articles indexed in databases are given descriptors or subject headings, it is often helpful to use these to refine your search, or to find more articles on your topic.
While it is possible to conduct a subject search in most databases, it is sometimes difficult to know what the exact subject is. To find out the what the appropriate subjects/descriptors are for your topic, you can consult the thesaurus or subject heading list for the specific database you're using. Alternatively, you can start with a keyword search and look at the record of a relevant article to see what subjects are listed that may also be suited to your topic.

In the above examples from Academic Search Premier, both the data for a specific article and the thesaurus show that the correct subject term (and possibly the easiest way to search for relevant articles in this database) for interest groups is pressure groups.