Mounting points are the threaded bosses on your frame and fork that let you attach bottle cages, racks, fenders, and other accessories. Gravel bikes range from about 4 to 20 mounting points, and the right number depends on how you ride.
If you mostly do fast day rides or gravel racing, 4–8 points is plenty — that covers two or three bottle cages with little else. For all-around riding that might include commuting or light touring, 8–12 points is the sweet spot, typically giving you three bottle positions plus fender and rack mounts.
Bikepackers and long-distance adventurers should look for 12 or more points, including fork blade mounts (critical for front bags), under-downtube bottle bosses, and full rack eyelets. Just be honest about what you'll actually use — paying for mounts you never need adds cost, and unused bosses are just extra weight on the frame.