In computer science, a library is a collection of resources used to develop software.^{[disputed – discuss]} These may include pre-written code and subroutines, classes, values or type specifications.

Libraries contain code and data that provide services to independent programs. This encourages the sharing and changing of code and data in a modular fashion, and eases the distribution of the code and data. Some executables are both standalone programs and libraries, but most libraries are not executable. Executables and libraries make references known as links to each other through the process known as linking, which is typically done by a linker.

Most compiled languages have a standard library although programmers can also create their own custom libraries. Most modern software systems provide libraries that implement the majority of system services. Such libraries have commoditized the services which a modern application requires. As such, most code used by modern applications is provided in these system libraries.

In object-oriented programming (OOP), inheritance is a way to reuse code of existing objects, or to establish a subtype from an existing object, or both, depending upon programming language support. In classical inheritance where objects are defined by classes, classes can inherit attributes and behavior from pre-existing classes called base classes, superclasses, parent classes or ancestor classes. The resulting classes are known as derived classes, subclasses or child classes. The relationships of classes through inheritance gives rise to a hierarchy. In prototype-based programming, objects can be defined directly from other objects without the need to define any classes, in which case this feature is called differential inheritance.

The inheritance concept was invented in 1968 for Simula.

A subclass, heir class, or child class is a modular, derivative class that inherits one or more properties from another class (called the superclass, base class, or parent class). The properties in question vary from language to language, but commonly include class data variables, properties, and methods or functions. Some languages support the inheritance of other properties as well. For example, in Eiffel, contracts which define the specification of a class are also inherited by heirs. The superclass establishes a common interface and foundational functionality, which specialized subclasses can inherit, modify, and supplement. The software inherited by a subclass is considered reused in the subclass.