This is about how hard is it to comprehend the game from start.
In easy mode you start in a ship with only one component - so you have to learn only one from start, and will figure out others later as you get them.
In medi mode your start ship has seven different kinds of components.
In hard mode your ship has fifteen random components, and I don't know which.
It's always equally easy to play the game. You can never really lose for real: ships never kill each other completely, and as long as you have any kind of ship - you can start working on making it better!