A loan of trust. What’s owed back is fixed, regardless of what happens to it.
Amanah names one of the two basic postures Islamic contract law recognises for handling someone else’s money: holding or lending it purely as an act of trust, with no exposure to risk or reward. The amount is fixed and returned as-is, no profit-sharing, no loss-sharing, and no interest charged on top. Whoever holds an amanah is accountable for its safekeeping, not for whatever a venture built with that money might do.
This sits opposite mudarabah, the profit-and-loss-sharing structure used when money is meant to fund actual risk-bearing enterprise. The two exist as a deliberate pair: custody calls for amanah, investment calls for mudarabah, collapsing the two, treating a safekeeping arrangement as though it were an investment or vice versa, is exactly the kind of category error that later confuses who’s accountable for what.
Source: A Primer on Islamic Finance, CFA Institute Research Foundation, 2009.