Selling investments at a loss to offset taxable gains.
Tax-loss harvesting means realizing a loss on an investment to cancel out capital gains — and up to a limited amount of ordinary income — reducing your tax bill. You then reinvest in a similar but not "substantially identical" holding to stay in the market. The wash-sale rule prevents claiming the loss if you rebuy the same security within 30 days.
Selling a losing fund to offset gains, then buying a comparable fund, harvests the loss.