Lip reading is a technique of understanding spoken language with out hearing its sounds. Practioners learn the phonemes associated with the shape and attitude of the mouth and infer words from what they view.
Although lip reading is commonly taught, it does not lead to perfect understanding. For instance the phase "Island view" would be lip read as "I love you". Critics claim that 50% understanding of language by lip reading is about the maximum achievable. This would presumably vary from language to language.