'Applaud' can mean the physical act of clapping hands together, either by a single person or a number of people; it can also mean to praise, to say positive words of admiration for a person or thing. I would usually use 'applaud' in place of praise for a large number of people, when the admiration and positive reaction was general and not well-defined. It is also used for an event that happens that is met with general approval. "The reform of the old law was applauded by the general public." 'Praise' would be used more if there were specific words said by a person or persons. "The new film was praised by critics." "The play 'Hamlet' has been praised by critics and audiences alike."