Brumation is the reptile equivalent of mammalian hibernation in which reptiles over 1 year old experience a natural metabolic slowdown (usually during winter). During this time your gecko will stop eating/drinking/pooping, act sleepy, and may not even leave their hide for weeks on end. It’s horribly boring, but nothing to be concerned about.
During leopard gecko brumation, make sure to keep your gecko’s water bowl filled with fresh water and if they wake up, feel free to offer a few insects. You should also weigh them once a week. If they’re losing a lot of weight, they may have a parasite problem. Deworming before brumation can prevent this issue.