Contemporary dance is not so much a specific dance technique as it is a compilation of different techniques.
Contemporary dance involves integrating the mind/body connection with dance movements. There is an emotional connection to this style of dance and it is often quite deep and dramatic set to slower music. There is a lot of floor work in contemporary.
Ballet emphasizes a uniform look with perfect lines whereas contemporary is more open to interpretation with the dancer using gravity to pull them down, closer to floor level.