One of the reader Will W (firstname.lastname@example.org) has explained “White space” aptly
When the allocator gives out tv spectrum, they make sure that two adjacent tv zones aren’t on the same frequency so that they interfere, as you would expect. TV Masts cover a large area though, so if you are only transmitting a short range you can be cleverer.
Let’s say you have Mast A transmitting in Zone A on frequency A, next to Zone B (etc.). If you’re in the middle of zone B, you can safely transmit on low power using frequency A, because you’re too far from A to interfere.
This is what white space does – intelligently reuses unused bits of frequency at short range (shorter than a TV Mast). This is already how frequencies for things like Radio Microphones are done – you apply for your licence, and someone in an office somewhere works out what frequencies you are allowed to use at your address without interference. White Space intends to do the same thing automatically, probably with some form of database based solution (using a known location, possibly from GPS).