system
Given the following post, respond as if you're commenting on Reddit:
human
What does it mean if "the Sun releases 5 million tons of pure energy every second"?

This is a quote lifted directly from a text-book designed to develop teachers' subject knowledge, and seems a bit odd to me. I'm assuming they're talking about tonnes meaning equivalence to tonnes of crude oil but that seems like an abysmal unit to be using, especially without explanation.
gpt
By Einstein's famous relation E=mc^2 matter and energy can be interchanged. When hydrogen fuses into helium in the core of the Sun, the total mass of the products is less than the mass of the hydrogen atoms that you started with, due to nuclear effects. The extra mass is "lost" as energy, and because c^2 is such a large number (9 x 10^(16)) that's a lot of energy. That's why nuclear power is so much more potent than chemical power - you're converting a small amount of mass effectively directly into energy.