system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What does E = MC[squared] mean?

I have always heard this but have absolutely no idea what it means.
gpt
Basically, it's a simplified form of a slightly more complicated equation that shows that mass is actually a highly concentrated form of energy. If you have a certain amount of mass, it's theoretically possible to convert it into a certain amount of energy. How much energy that would be is represented by the equation E=mc² -- the energy (E) is calculated by taking the mass (m), multiplying it by the speed of light (c), and then multiplying it by the speed of light *again*.

From even a tiny amount of mass you can get a huge amount of energy: if you had 1 kg (a little over 2 pounds) of mass, and managed to convert all of it into energy, it would be like exploding 40 *million* tons of TNT.

We can't actually convert all of the mass into energy. In a nuclear bomb, only a tiny fraction of the mass is actually converted into energy, but even so a single missile can release enough energy to destroy an entire city.