It’s just a name. Whatever they call it, as long as you’re playing without risking your own money, that’s automatically demo play. No need to complicate it. The effect it has on you is your own thing, but the obvious purpose of demo play is to let you learn the game and get an idea of how it works before you start risking real money.

Personally, I don’t even bother with demos anymore. Most games are easy to learn, and honestly you can just watch a few YouTube videos and already know how the game is played.