Many search engines support what is called a "wildcard" search; basically, this means you can substitute the asterisk symbol for a word within a key phrase, essentially telling the search engine that you'd like it to search for a word that is commonly associated with another word that you specify.
Here's how it works in Google:
three*mice will bring you back several results: three blind mice, three button wheel mouse (Google seems to search for variations on the last word you use), three button mice, etc.
Of course, this is a pretty generalized search phrase, but the wildcard search can really come in handy if you're not sure of what you're looking for, but you know the general gist.
For example, say you're looking for the flying habits of several different kinds of parrots. You could use this search string: "flying patterns" *parrot. This would tell Google (and most other search engines on the Web) that you're looking specifically for the phrase "flying patterns" (use those quotation marks to delineate a phrase), plus different kinds of parrots.
The wildcard search usually works in Yahoo, Ask, and Bing, with varying results. It's always best to try searches in several search engines, as each of them draw their results from very different indexes and can serve up drastically variable results (see Do Search Engines Search The Entire Web? for a more detailed discussion on this subject).