Original: Monophysitism (from the Greek monos meaning 'one, alone' and physis meaning 'nature'), or Monophysiticism, is the Christological position that Christ has only one nature (human-that-evolved-into-divine), as opposed to the Chalcedonian position which holds that Christ maintains two natures, one divine and one human.
Simplified: It says that Christ only has one nature, namely  the divine one.