A commodity has two characteristics.
The first charactaristic is its use as a thing. It satisfies a human need or want, directly as a consumer product, or indirectly as a production ingredient for consumer products. This charactaristic is necessary but not sufficient. There were useful things before there were commodities.
The second charactaristic is its worth in the market system. In particular, commodities exist for this purpose AS MUCH AS for their usefulness. The market value of a commodity is the only reason it is produced by capitalists, who have no use for 50000 gallons of olive oil for example.
These two elements of a commodity are in tension with one another, and from this embryo of contradiction, all of the contradictions in capitalism are formed.
Everything that happens in the market is subjected to this bifurcation of usefulness and exchange value. Real estate, goods, machines, and even human labor.