  This chapter defines and presents different kinds of software ecosystems. The
focus is on the development, tooling and analytics aspects of software
ecosystems, i.e., communities of software developers and the interconnected
software components (e.g., projects, libraries, packages, repositories,
plug-ins, apps) they are developing and maintaining. The technical and social
dependencies between these developers and software components form a
socio-technical dependency network, and the dynamics of this network change
over time. We classify and provide several examples of such ecosystems. The
chapter also introduces and clarifies the relevant terms needed to understand
and analyse these ecosystems, as well as the techniques and research methods
that can be used to analyse different aspects of these ecosystems.
