Gravity points are shorthand for the digits after the decimal point in a specific gravity reading — a wort at 1.050 is commonly called "50 points," and one at 1.065 is "65 points." It's an informal unit brewers reach for constantly, but it's not just a casual nickname; it has a genuine mathematical reason to exist.
Why this shorthand is more than convenience
Gravity points are additive across volume in a way specific gravity itself isn't — total gravity points in a vessel (roughly, points times volume) stays conserved when you split, combine, or dilute batches, which is exactly the math the dilution and blending calculator runs under the hood. Trying to do that same math directly in specific gravity terms (1.050, 1.065, and so on) is needlessly awkward; converting to points first makes the arithmetic straightforward.
Where this shows up in practice
Any time a recipe or a brewer talks about diluting a too-strong wort, blending two batches to a target gravity, or estimating how much a small water addition will move OG, they're really doing gravity-points arithmetic, whether or not they use that specific term for it. Learning to think in points rather than full gravity readings makes a lot of recipe-scaling math noticeably less error-prone.