A B-tree is a data structure that consists of ordered nodes arranged in a balanced tree. Each node contains keys (the numbers that you see) and children (the nodes directly below it).
Nodes are sorted to the left, middle, or right depending on whether their keys are less than, in between, or greater than the parent's keys. Add some values to the demo for a visual demonstration of this.
The root is the top node, internal nodes are in the middle, and leaf nodes are on the bottom. Using this terminology, a valid B-tree of order m obeys the following rules:
B-trees allow you to quickly search for values, and they're often used in databases and file systems.