Body — or weight — describes the sensation of weight and texture that a wine gives in the mouth. Think of the difference between skimmed milk, whole milk, and cream: all three are white liquids but feel completely different on the tongue. Light-bodied wine is delicate and fleeting, medium-bodied is balanced, and full-bodied wine gives a rich, heavy sensation.
Several factors affect body: alcohol is the strongest contributor — more alcohol means more body. Residual sugar, glycerol, and degree of extraction also play a role. Warmer climates produce riper grapes with higher sugar content that ferments to higher alcohol, which explains why wines from warm regions are often perceived as fuller-bodied.