Public Domain consists of all inspired work and other information (Music, invention, artwork, writing, technology, etc.,) on which no one i.e. Person or Organization claims an ownership. Such information is considered to be part of Public's inheritance and anyone can exploit them for their needs without any restriction.

Public Domain can be General information which includes facts, ideas, templates, etc. which could be used by anybody for their needs. Public domain may also be works that may be donated for Pubic Domain. Some of the works by Government also falls under Public Domain.

Copyright was designed to get a financial spur to the owner while works in public domain are present for the public to use them without any financial constraint. Copyrighted works fall under public domain once their copyright period is expired.

Not all the information available on the internet fall under Public domain contents. But all works published in US before 1923 are in the Public Domain. The classic examples would be Shakespeare and Sherlock Holmes mysteries. Bookstores utilize the public domain by reprinting works that are public domain.

The public domain is a space where intellectual property protection does not apply. When copyrights and patents expire, innovations and creative works fall into the public domain.

They may then be used by anyone without permission and without the payment of a licensing fee. Publicly owned national parks are also considered by many to be public domain lands. Because of the extensions of the terms of both copyrights and patents, and the privatization of lands and other resources owned by the Federal Government, little is now entering the public domain.

Since the public domain is a treasure trove of information and resources to be used by future generations, many advocates are concerned that its stagnation will make it more difficult for future generations to find creative inspiration.

Copyleft is a way to make program free software and require those who distribute improved versions of it to make them free also.

The Copyleft principle is simple. When one programmer creates program, he has a copyright in that software. Legally, he has the power to control its use, redistribution, and modification. By releasing it under a copyleft license he makes the software available to the public in freedom, while requiring every released program that reuses his code to be free in the same way.

Copyleft encourages the user community to contribute to the improvement of the free software, by closing off the temptation to make those improvements proprietary. Meanwhile, companies are free to use, improve and redistribute the software, just like individuals.