This is distinct from the standard of deferred payment function which requires acceptability to parties one owes a debt to, or the unit of account function which requires fungibility so accounts in any amount can be readily settled. It is also distinct from the medium of exchange function which requires durability when used in trade, and a minimum of opportunity to cheat others.
When currency is stable, money can serve all four functions. When it isn't, such as during times of hyperinflation or when complex and volatile forms of financial capital are involved, it becomes important to identify alternative stores of value, of which common ones are:
While these items may be inconvenient to trade daily or store, and may vary in value quite significantly, they rarely or never lose all value. This is the point of any store of value, to impose a natural risk management simply due to inherent stable demand for the underlying asset. It need not be a capital asset at all, merely have economic value that is not known to disappear even in the worst situation. In principle, this could be true of any industrial commodity, but gold and precious metals are generally favored because of their demand and rarity in nature, which reduces the risk of devaluation associated with increased production and supply.