Software is a general term that is used to describe a collection of computer programs that perform tasks on a computer. At its lowest level, software consists of a machine language that is specific to an individual processor, but usually software is written in a higher level language such as C++.
The majority of software can be divided into three types: system software, which helps run the computer (including operating systems like Microsoft Vista, and Mac Leopard); programming software (tools to assist the programmer in writing software, like Microsoft Visual Studio and Altova's XML Spy); and application software that lets end users accomplish one or more tasks (including, for example, Adobe Photoshop Lightroom and Microsoft Office).
Software can also be divided into two other business camps. One is the for profit camp where software is sold via licensing agreements; these include most of the software listed above, and the other is the non-profit or open source software camp where the licensing requires that it and all derivatives remain freely available to all; these include Linux, GIMP, and MySQL.