Cycle counting is counting a small, rotating set of inventory items on a regular schedule, so every item is counted several times a year without closing for a full stock take.
Items are usually counted by value: A items monthly, B quarterly, and C once or twice a year. Counts are done blind — without seeing the expected quantity — and any variance is recounted before it's adjusted.
It catches errors days or weeks after they happen, instead of months later at a year-end count.