(1) The state of a computer, usually determined by which programs are running and basic hardware and software characteristics. For example, when one speaks of running a program in a UNIX environment, it means running a program on a computer that has the UNIX operating system.
One ingredient of an environment, therefore, is the operating system. But operating systems include a number of different parameters. For example, many operating systems allow you to choose your command prompt or a default command path. All these parameters taken together constitute the environment.
Another term for environment in this sense is platform.
(2) In DOS systems, the environment is an area in memory that the operating system and other programs use to store various types of miscellaneous information. For example, your word processor may use the environment area to store the location of backup files. You can view or modify the environment with the SET command.