Empty Horizon is quite self-explanatory: there is no land in sight, and there never will be... unless you build one!
You are in the middle of a deep ocean, alone on top of a small wooden platform.
You will have to make good use of whatever you have, which is just about enough to get you started.
You will have to find food, farm blocks, craft tools and get more resources as you progress.
It is an infinite experience with no end goal - you can expand your platform, reach the bottom, explore your surroundings, search diamonds and even go to the nether!
Just don't lose your platform, will you? :)