Delta hedging
Trading the underlying so a position's total delta stays near zero, which keeps small price moves from changing its value much.
An option's delta says how much its price moves for a $1 move in the underlying. A trader who holds options can offset that exposure with shares: short stock against long calls, for example, so gains on one side roughly cancel losses on the other.
The offset does not stay exact. As the underlying moves, each option's delta changes by its gamma, so the hedge has to be adjusted, buying or selling more shares. Those adjustments are the flows that gamma exposure models try to estimate.
Illustrative example (hypothetical numbers, not a real trade): a trader is long 20 calls with a delta of 0.50, which is 20 × 0.50 × 100 = 1,000 shares of exposure, and shorts 1,000 shares against them. The stock rises $1 and the calls' gamma of 0.05 lifts their delta to 0.55. Exposure is now 1,100 shares, so the trader shorts 100 more to stay neutral.