What is the definition of value in art?

Value The lightness or darkness of tones or colors. White is the lightest value; black is the darkest. The value halfway between these extremes is called middle gray. Space An element of art by which positive and negative areas are defined or a sense of depth achieved in a work of art .

I'm pretty sure value is like, the thickness or darkness of a color, or tones. Such as white being the lightest, black the darkest. 

The region of the united states where beef and hog production is prevalent is the midwestthere are 12 states in this area including  illinois,  indiana,  iowa,  kansas,  michigan,  minnesota,  missouri,nebraska,  north dakota,  ohio,  south dakota, and  wisconsin. all of these states are known for their meat and such products.