Colour gamut is the range of colours a system can actually display or capture — like the size of the palette a painter has access to. Every screen, every camera, every colour space has a specific gamut, and the differences between them are huge. The standard reference is the CIE 1931 chart showing every colour visible to the human eye; modern colour gamuts each cover some fraction of that.
The benchmarks worth knowing. sRGB / BT.709 is the historical web and HD-TV gamut, covering about 36 % of all visible colours. DCI-P3 is the cinema standard, covering about 45 % — most modern premium TVs and iPhones can reproduce it fully. BT.2020 is the 4K HDR gamut, covering about 76 % — far wider than anything else, but no consumer display fully reaches it yet (the best premium OLEDs hit ~70–80 %). When someone says "this TV has 95 % DCI-P3 coverage", they mean it can reproduce 95 % of the DCI-P3 gamut.
Why gamut matters for a streaming product. A 4K HDR film mastered in BT.2020 contains colours that BT.709-only TVs literally cannot show — they'll look washed out. The fix is gamut mapping at the encoder or player, where saturated colours outside the smaller gamut are pulled back into the achievable range; done well it looks reasonable, done badly it loses the impact of HDR completely. The pragmatic delivery rule: master in the widest gamut your content deserves (BT.2020 for HDR, DCI-P3 for premium cinema, BT.709 for everything else) and let the player do gamut translation. Don't claim "wide colour gamut" in marketing unless your pipeline actually preserves it end to end.
