a deputy is a person who helps someone do their job when they are not there. "deputy" is a rank or title. it usually refers to someone who is "second-in-command". for example: a "deputy master" is someone who will take over the responsibilities of the master when the master is not there. a "deputy conductor" will conduct an orchestra when the main (principal) conductor is not there. it is similar to an "assistant". someone who is working as a deputy will deputize (stand in for someone else).