Imagine you have a big party and you want to invite people who live near your house. You might write down a list of all the streets where your guests live. But what if there are too many streets to fit on your list? You might decide to only write down the major streets where most of your guests live.
In math, we're sometimes interested in studying sets of numbers. But some sets of numbers are too big or too complicated to study directly. For example, the set of all real numbers between 0 and 1 is infinite and can be very complicated. We might only be interested in a smaller, simpler set of numbers that can still tell us something interesting about the bigger set.
This is where Baire sets come in. A Baire set is a simpler, smaller set of numbers that can still give us information about a bigger set of numbers. Just like how we might write down only the major streets on our party invitation list, a Baire set focuses on the most important or informative parts of a larger set of numbers.
More technically, we say that a set of numbers is a Baire set if it's "dense" in a certain sense. This means that there are lots of numbers from the bigger set inside the Baire set. For example, the set of all rational numbers (numbers that can be written as a fraction of two integers) is a Baire set inside the larger set of all real numbers.
So why do we care about Baire sets? They're useful for studying things like continuity and convergence in math. And just like how inviting only certain streets to our party helps us manage our guest list, focusing on Baire sets helps us manage and simplify the study of complicated sets of numbers.