As you’re creating something, you may wonder what copyright infringement actually is. It’s necessary, if you’re creating a work -- albeit written, musical, videos, software or some other form -- that you know the definition of copyright infringement. This issue is very complicated, and not very easily spelled out in plain English.
Copyright infringement is defined by the jurisdiction -- the United States of America has different copyright laws than the United Kingdom, or Australia, or Russia, or even China. Because of this fact, you should first, before anything else, check the laws in your jurisdiction (country, city and province) before using something that isnt in the public domain.
For our definition of copyright infringement, works in the public domain arent copyrightable. Works that arent copyrightable include ideas, works that arent eligible (150 years-old documents, or older -- think Beethoven and Frankenstein), data that isnt categorized in a creative way (this could be a database, such as a phone book or other publicly-accessible data), or items that the owners have specified creative commons copyrights.
As you can see, copyright law is rather complicated. Wikipedia.org gives us the definition of copyright infringement as: Copyright infringement (or copyright violation) is the unauthorized use of material that is protected by intellectual property rights law particularly the copyright in a manner that violates one of the original copyright owner's exclusive rights, such as the right to reproduce or perform the copyrighted work, or to make derivative works that build upon it. The slang term bootleg (derived from the use of the shank of a boot for the purposes of smuggling) is often used to describe illicitly copied material.
Our definition of copyright infringement includes the works of creative commons. Creative commons is an organization that allows for the copyright author to determine the uses available for people who want to use their works -- for such items as for audio, images, video, text, educational materials, and software. It allows for the copyright owner to allow people to use their works for non-commercial, commercial, no derivatives, share alike, or just by giving attribution. Creative Commons is a license granted by the copyright holder, and can be used in both online (electronic Internet) works and offline works.
There are many places you can go to get a definition of copyright infringement. The most reliable definition of copyright infringement would be from your local copyright lawyer -- they will know exactly what in your jurisdiction is legal or not, and how you can use other peoples works or protect your own.
The real definition of copyright infringement comes from your jurisdictions statutes. In the United States of America, our jurisdictions copyright laws are contained in Title 17 of the United States Code, §501 - §513. You can also find a definition of copyright infringement through such organizations such as the European Union or World Trade Organizations.
Source: Definition of Copyright Infringement