Okay, so imagine you have a big box of toys. You want to keep track of all the toys in the box, so you make a list of everything that's in there.
That's kind of what a "basis" is in math. Instead of a box of toys, you have a bunch of numbers or shapes or other math things, and you want to keep track of them. So you pick a few of them to be your "basis" - it's like they're the most important toys in the box.
You can describe everything else in terms of the basis toys - just like you can say "the red truck is next to the blue ball" instead of trying to describe every single thing in the box.
Janet basis is a specific kind of basis that's used in something called "topology" (which is a fancy math word for studying shapes and spaces). It's named after a mathematician named Janet who figured out some stuff about how to pick a good basis. Basically, a Janet basis is a fancy type of basis that helps you understand certain kinds of shapes and spaces better. Does that make sense, buddy?