Echelon (signals intelligence)

Echelon is like a big net that catches signals that are sent through the air, like underwater sounds or radio waves, and then collects them and stores them. It's like putting a big net out in the ocean and seeing what kind of fish you can catch. In this case, the fish are signals and the big net is echelon. It listens to all kinds of signals, and then stores them for governments or militaries to go back and look at.