An environment is a complex of surrounding circumstances, conditions, or influences in which a thing is situated or is developed, or in which a person or organism lives, modifying and determining its life or character.

In biology, ecology, and environmental science, an environment is the complex of physical, chemical, and biotic factors that surround and act upon an organism or ecosystem.
The natural environment is such an environment that is relatively unaffected by human activity.
environmentalism is a concern with the preservation of the natural environment, especially from human pollution, and the ethics and politics associated with this.
In social science, environmentalism is the theory that the general and social environment is the primary influence on the development of a person or group. See also nature versus nurture.
Another social science concept is the Social environment, also known as milieu.
In computing, an environment is the overall system, software, or interface in which a program runs, such as a runtime environment or environment variable, or through which a user operates the system, such as an integrated development environment in which the user develops software or a desktop environment.
In mathematics and programming languages, an environment is a set of variables that have been bound. Some kinds of environment also map variable names to values or to types. An environment gives meaning to free variables.
In art, an enviroment is a kind of installation, an artwork that surrounds the observer, and sometimes allows the audience to modify it or interact with it. The first environment was probably the installation of wool strings and playing children by Marcel Duchamp in a group exhibition around 1945.