What are boot params?
A boot param is a special number which allows you (if used appropriately, see below) to go directly to a specific part of a game. These boot params are mostly useful for debugging and playtesting a game; you get teleported to a certain situation in a game, with some of the items appropriate for it. It is not always possible to continue and complete a game from this, because you may lack important items. But for us developers, it's very helpful, because we can quickly get to trouble spots in a clean state, and try to reproduce any bugs you report to us.
These boot params do not exist by chance or magic: they were put into the game data by the original developers of the games, and were meant for exactly the same purpose we use them for: to help in debugging the game. Of course, they also make a nice cheat system (with some caveats, as I tried to outline above).