Institutional stock loan is quoted as a rebate rather than a fee. The short posts cash collateral, the lender invests it at short-term rates and rebates part of the interest back. For an easy-to-borrow name the rebate is close to the risk-free rate; as demand rises the rebate falls and eventually turns negative, at which point it is simply a borrow-fee by another name.
Retail accounts generally never see the rebate at all: the broker keeps the collateral interest and quotes only the fee.
Example: short rates are 4.8%. An easy-to-borrow name rebates 4.55%, so the short earns 4.55% on collateral. A hard-to-borrow name rebates minus 25%, meaning the short pays 25% a year net.
Related: borrow-fee, securities-lending, hard-to-borrow, easy-to-borrow, short-selling