Definition of theme - Environment

From mac book dictionary:
1.The surroundings or conditions in which a person, animal, or plant lives or operates.
For example: Hippopotamus living in near rivers so as to cope with the hot temperatures in the South Africa and to cool down in the mud or river.

2.The natural world, as a whole or in a particular geographical area, esp. as affected by human activity.
It is which most people think of about environment.

From :http://en.wikipedia.org/wiki/Desktop_environment
A desktop environment typically consists of icons, windows, toolbars, folders, wallpapers, and desktop widgets.
Software which provides a desktop environment might also provide drag and drop functionality and other features which make the desktop metaphor more complete. On the whole, a desktop environment is to be an intuitive way for the user to interact with the computer using concepts which are similar to those used when interacting with the physical world, such as buttons and windows.
While the term desktop environment originally described a style of user interfaces following the desktop metaphor,it has also come to describe the programs that provide the metaphor itself.(Words in bold is the key words)
For example:The Microsoft computer always have a desktop to put things like folders and icons etc.
From:http://en.wikipedia.org/wiki/Environment_(biophysical)

The biophysical environment is the symbiosis between the physical environment and the biological life forms within the environment, and includes all variables that comprise the Earth's biosphere.
The biophysical environment can be divided into two categories: the natural environment and the built environment, with some overlap between the two. Following the industrial revolution, the built environment has become an increasingly significant part of the Earth's environment.(Words in bold is the key words)
From this i can tell that there are also the natural and built environment,for example a rain forest is a natural environment while a city is a built environment. Overlap environment will be most of Singapore parks and garden.

To conclude, i think that environments are places that people,plants and animals live in and there is also different types of environment like built,natural or both and that the computer desktop is also an environment.