
OpenStack is a cloud operating system that controls large pools of compute, storage, and networking resources throughout a datacenter, all managed and provisioned through APIs with common authentication mechanisms.
A dashboard is also available, giving administrators control while empowering their users to provision resources through a web interface.
Beyond standard infrastructure-as-a-service functionality, additional components provide orchestration, fault management and service management amongst other services to ensure high availability of user applications.

Source : https://www.openstack.org/software/
OpenStack is broken up into services to allow you to plug and play components depending on your needs. The openstack map gives you an “at a glance” view of the openstack landscape to see where those services fit and how they can work together.
Why would you start with OpenStack?
How do you get started with OpenStack?