Capability is the capacity to do something!
In the context of In the JT-NM reference architecture Capability is the representation of a “usefully minimal” item of functionality provided by a device (a device can be software only or hardware and software) providing just enough information for an application to be suitably paired with the device. For example, a compression codec “device” could offer a capability the network.
See also: JT-NM, AMWA, NMOS, Flow, Grain, SMPTE 2110