Particular prices are sometimes regarded as benchmarks for a wider range of prices, this is most common with commodities.
This is usually because a single commodity exists in many forms that can be distinguished by different properties or quality. This means that investors need to be clear what price they are following, and this usually means the price of the commodity in a form that is closely specified and traded on an exchange.
For example, the price of crude oil generally means the price on one or another of certain crude oils that are regarded as benchmarks or a composite of them.