National technical means of verification (NTM) is a way that countries like to keep an eye on what's happening in other countries. It's like having a big eye in the sky that can see everything that's going on. With NTM, countries can use things like satellites or other special equipment to watch what other countries are doing. This can include things like testing weapons, building new buildings, or moving troops around.
Think of it like a game of hide-and-seek. Everyone is hiding, and the person who is seeking has to find them. NTM is like giving the person who is seeking a special pair of glasses, so they can see everyone who's hiding.
However, it's important to remember that not all countries are allowed to use NTM. Sometimes countries will agree to certain rules that say they can't use certain technologies to spy on each other. If a country doesn't follow these rules, there can be consequences like getting in trouble with other countries.
Overall, NTM is a way for countries to keep an eye on what's happening in other countries, but it's important to use it in a fair and appropriate way.