The idea of public domain opened the door for the general people to get closer to the greatest creations around the world. There has been different values and importance regarding to the term most of the time; however, they are not always true depending the status and availability of the work we are talking about.
Public domain is the best way for accessing into the cultural and artistic world. If you want to take a look at the oldest Greek scrolls or listen to the symphonies of Mozart, you have to thank the system of public domain as these have been accessible because of this law. The same thing goes for the original ideas and theories that are included within the general education system.
Beside the expiration of the ownership, all the creative products that do not fall under any of the copyright, trademark and patent structure are included in the public domain category. And as all the work with creativity and new ideas of both world- science and art- do not require copyright, there is no shortage of new materials in the domain. Also all the works that has been abandoned from the copyright law are also included in the public domain.
The working area of public domain is very wide and it has certain value on the society. However, this is not applicable to all creative works. The major importance of the term is in building up a new trend or knowledge. If you want to develop a new theory that requires a lot of research and support from others, it is a good thing that you keep it open for everybody to work on it.
For example, consider about Linux. This was a new operating system that first came out of the traditional copyright principles of other companies. From the starting, this OS was an open source program and kept its door open for everybody who were interested in developing this new OS.