Imagine you have a big box of crayons with lots of different colors. You can draw pictures with all the colors you want! But sometimes, when you try to draw a specific color, you notice that your crayons don't have the exact shade you need.
Well, this is kind of like what gamut means when talking about colors. Gamut is like the range of colors that a device, like a printer or a computer monitor, can produce. Just like your box of crayons, these devices have limits in the number of colors they can create.
So, even if you want a very specific shade of blue, if your device isn't capable of producing it, then you'll have to settle for the closest color it can produce. This is why sometimes what you see on your computer screen looks a bit different when you print it out.
Ultimately, gamut is the range of colors that any device or medium can produce, and it determines the colors you can see in your pictures or videos.