Deadband is a term commonly associated with the positional accuracy of a servo. Servos are typically closed loop (minus a few exceptions which raises the question whether or not those rare cases should be considered servos or not) which means they can be told to go to a specific position. The deadband is essentially the size of the bullseye - how accurately must the servo position itself based on what the controller called out to satisfy the request. Servos with very small deadbands are shooting for extreme accuracy and are excellent for high precision applications whereas servos with wide deadbands are less picky about positional accuracy but are able to get to an idle state and pull less current once they get close to the desired position.