Imagine that you have a bunch of balls that you want to put into a box. But you don't want to just throw them in randomly, you want to fit as many balls as possible into the box without any of them overlapping or going outside of the box.
That's what we call "sphere packing." "Sphere" just means "round ball" in math talk.
Now, if you only had a few balls and a really big box, you could probably just put them in there all nice and neat without much trouble. But what if you had a TON of balls and a relatively small box? Would you be able to fit them all in there?
Well, that's where "finite sphere packing" comes in. It's when you're trying to fit a specific number of balls into a specific sized box.
It turns out that mathematicians have studied this problem a lot and have come up with some pretty cool ways to figure out the maximum number of balls you can fit into a box.
One of the most famous examples is called the "hexagonal close packing" arrangement. Basically, it involves stacking layers of balls so that each ball is touching six other balls around it, kind of like the cells of a honeycomb. This arrangement turns out to be really efficient and allows you to fit a LOT of balls into a relatively small space.
Of course, there are other ways to arrange the balls as well, and mathematicians are always coming up with new and better ways to do it. But the basic idea is the same: you want to fit as many balls as possible into the box without any of them overlapping or going outside of the box.