In the United States, a patents is “the right to exclude others from making, using, offering for sale, or selling” or importing an invention issued by the U.S. Patent and Trade Office (USPTO), usually for a period of 20 years. According to the USPTO, "there are three types of patents:
1) Utility patents may be granted to anyone who invents or discovers any new and useful process, machine, article of manufacture, or composition of matter, or any new and useful improvement thereof;
2) Design patents may be granted to anyone who invents a new, original, and ornamental design for an article of manufacture; and
3) Plant patents may be granted to anyone who invents or discovers and asexually reproduces any distinct and new variety of plant."
For more detailed information about patents and other kinds of intellectual property protection (trademarks, servicemarks, copyright),visit the the USPTO's Generral Patent Information website. The University of Michigan's "Michigan Engineering" website also offers a set of videos that describe patent rights, what can be patented, obtaining a patent, and patent infringement and litigation
The USPTO offers a suggested procedure for preliminary patent searching of U.S. and European patents called the Seven Step Strategy. It has also designated a nationwide network of public, academic and state libraries as Patent Trademark Resource Centers (PTRCs) that have experts trained to use search tools that are only available on site and to help the public with patent information.
Additional online sources that can help you with patent searches include: