Well, imagine you and some of your friends are playing on the playground, and you all have different kinds of toys. One of your friends has a really cool toy that everyone wants to play with, but your other friend doesn't have any toys at all.
A social floor means that we want everyone to have at least something on the playground to play with, even if it's not the coolest or fanciest toy.
It's like making sure that everyone has a basic level of things they need to live a happy life, like a safe place to live, enough food to eat, and access to healthcare. These things are important to make sure that everyone has a fair chance to be happy and healthy.
So just like how we want everyone to have something to play with on the playground, we want everyone to have a social floor of basic needs that are met.