A price is simply a ratio of something in terms of something else. It need not necessarily be in terms of a fiat currency. The price of a certain watch may be ten pairs of a certain brand of shoes, or equivalently, an hour of consulting service of a certain expert, and so on. The ratios in terms of some goods become more prevalent due to their characteristics: durability, recognizability, divisibility, scarcity; these goods begin to acquire monetary recognition as individuals start accumulating them for the express purpose of exchanging them (as opposed to consuming them). These goods are traded more frequently than other goods due to their utility as media of exchange. The most traded good, thus, emerges as money, and market participants find it convenient to denominate prices in terms of this money, which, historically, has been gold.
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