Dance is a performing art form consisting of carefully chosen sequences of human movement. When speaking of the levels in dance, you are classifying them for their different physical aspects. The three levels of dance movement are high, middle, and low.
The level refers to the distance of the dancer to the floor, and some movements will entail you to be high up from the floor. Then in the middle, you work with your feet on the floor, and the low level includes floor work.
Dance also uses many different body movements such as stretching, bending, twisting, jumping, swinging, tilting, rocking, and collapsing. Dances, which include various levels, are far more interesting then if they only danced at one level. A mixture of levels can also be accomplished by having some dancers on the floor, while others are way up high.