Radio spectrum
The range of radio frequencies satellites use to communicate, allocated internationally and licensed nationally rather than owned.
Spectrum is the constraint that turns satellite operations into a regulatory business. Two systems on the same frequency over the same place interfere, so rights are coordinated through international processes that move on a far slower timescale than the companies applying to them. For a constellation operator, the filing is as much of a prerequisite as the rocket - and a granted allocation often carries deadlines to deploy, which shapes launch schedules as firmly as engineering does.
Spectrum and licensing recur throughout our archive of 688 articles, usually as the reason a deployment is timed the way it is - a dimension of the industry invisible in any launch manifest, including our own.
An orbital slot, which is a position in the geostationary ring rather than a frequency. The two are coordinated together for geostationary satellites, which is why they are so often conflated.