An IP-XACT component describes data of any component, both flat and hierarchical, hardware and software. Most importantly it describes components external interface, such as ports and parameters, but also internal features, such as remap state and memory maps. On the other hand, many properties are parametrizable, and thus tied to the external interface.
A component may also refer to non-IP-XACT files, such as HDL source files and documentation. Thus components are vital for integration with non-IP-XACT tools and formats.