underestimate the real value or ability of; "Don't sell your students short--they are just shy and don't show off their knowledge"
sell securities or commodities or foreign currency that is not actually owned by the seller, who hopes to cover (buy back) the sold items at a lower price and thus to earn a profit
an accumulation of jobs not done or materials not processed that are yet to be dealt with (especially unfilled customer orders for products or services)