barley: the hardy cereal grain and the plant that bears it, the cheaper everyday staple of the ancient world
Barley is a single, concrete thing, so this word has one meaning throughout the Hebrew Bible. What shifts from verse to verse is only whether the writer has in view the plant growing in a field or the harvested grain in a person's hand, and the word covers both without strain, exactly as the English word "barley" does.
Barley mattered because it was the poor person's grain. It grew on marginal land, ripened weeks before wheat, and cost far less, so it fed animals and the poor while wheat fed those who could afford it. That gap in value is why barley keeps turning up wherever the Bible measures worth or pictures scarcity: it is the grain you count out as a low price, hand over as a meager payment, or eat when better food has run out.
Because it ripened first, barley also marked the opening of the grain harvest and the calendar that went with it, from the spring firstfruits onward. The two shades below, the standing crop and the harvested grain, simply follow whether a verse is looking at the field or at the storehouse.