A software package is a bundle of one or several files that either are necessary for the execution of a computer program, or add features for a program already installed on the computer or network of computers. Software packages can either be in a standardised package format to be installed by a program that is integrated with the operating system, or be a self-sufficient installer. This latter approach is commonly used by distributors of commercial, proprietary and closed source software, particularly for installation on Microsoft Windows, and less often for Mac OS X, whereas more traditional, and particularly free Unix-like operating systems favour the use of standardised formats that are extensions of file archive formats.
The term software package is also used in object-oriented programming to name a group of related classes of a program. In this meaning, packages are especially useful to measure and control the inherent coupling of a program.
In a modular program, even outside OOP, the term "software package" may refer to any component (see also module) that can be integrated into the main program through a well-defined interface and, typically, by the end user. In other contexts, the integration must occur at source code level, therefore requiring the knowledge of a given programming language.