Unity with variety seems a bit self explanatory. There is some sort of repetition of objects, lines, colors, or textures that contains differences/variety and look unified as a whole. Variety in the repetition can be achieved through position, size, and proportion differences.
This art piece featuring painted sculptures of arms and legs definitely shows unity with variety. The individual elements are all lined up systematically and are of the same origin (line of heads and line of arms) however, each head is different in composition and color from the next, as is the same with the arms. Each is designed in such a way, though, that the piece is completely unified.