The spec you are seeing is an old, but still common spec in North America for TV true Peak levels and refers to -10dBFS. -10 dB “full scale”.
User “Mike. aka RS170a” (above) referred to Loudness Range EBU R128, but that is not actually measured in dB; it’s measured in units simply called “LU” as they are actually a ratio, so they have no quantifiable unit, per se.
A few years ago the EBU began to notice too much compression in TV shows, as online audio engineers tried to cram as much loudness into their shows as possible by using limiting amplifiers common in music production (because they made things louder, and chopped off any waves at whatever peak you set them for – in the case of tv shows, -10dbTP). Broadcasters only set out this peak limit to their content providers and it left a LOT of room for engineers (especially on commercials) to cram a LOT of energy into a waveform (picture big thick waves albeit not peaking above -10dB.)
The experience at home that commercials were way louder than tv shows. Again, the waves didn’t peak over -10dB, but the meters were slammed hard up against that limit the entire time.
The problem was, peak was a terrible way of controlling the actual experience of loudness, as that is experienced (at the human level) more as an average rather than a tiny peak when, for example, a gunshot goes off in tv show.
To counter this, a universal standard of R128 was developed (led largely by the Germans) and has been adopted by the FCC, the CRTC in Canada, and much of Europe. It actually allows for much higher peaks (up to -1dBTP).
These days, many tv stations haven’t updated their specs, though I have helped some companies make the transition. The new standard involves using a Dolby Media Meter which has a whole other algorithm for measuring loudness measured in LUFS or LKFS, where -23LUFS is the average they are looking for (which is you are curious, LUFS is “Loudness Units, referenced to Full Scale”)
Without purchasing a very expensive Dolby plug in, you won’t be able to determine this spec, but it looks like that’s not your problem because the broadcaster in question is still living in the dark ages.
So to answer your question directly, it means no peaks above -10dB on a meter that measures True Peak. If your broadcaster is asking for this spec, they are still in the dark ages, but you should meter the show to this in case they are metering the shows as they arrive in their QC process (very likely).
PS- I should add that I see that Waves has released a Loudness Meter. Forgive me for not being up on all the latest releases, but that’s good news for you at $399!
For reference, I am 43 years old and have mixed several hundred hours of television for NAT Geo, History, BBC, CBC, etc. and I am the head of Post Audio at Arcadia Entertainment in Halifax, Nova Scotia, Canada.