Any commodity or asset that holds it purchasing power into the future. It is important that the asset can be saved, retrieved and have a market to exchange at a later date.
Most commons stores of value:
The idea is to manage risk via a stable demand for the asset.
Over the last few years, people in cryptocurrency promoted Bitcoin as a store of value. Thus far it has not panned out. There is a claim that stablecoins can serve a similar purpose. Like Bitcoin, this has yet to materialize.