The term store of value is used to describe the property of an asset that is able to avoid depreciation over a long period of time. So to be considered a store of value, an asset should have its value either stable or increase over time - but never decreasing.
A good store of value will enable its owner to sell or exchange it on a future date for a similar or higher value than it was initially bought. Usually, this value is related to the asset’s market price or purchasing power (monetary value). But, in some cases, it may also be related to the asset’s liquidity (i.e., how easy it is to buy and sell it).