The term RE PLANES can be broken down into two words, 'RE' and 'PLANES'. The first word, 'RE', is a prefix meaning 'AGAIN' or 'BACK'. The second word, 'PLANES', is a noun referring to aircraft. Therefore, the term RE PLANES can be interpreted as 'aircraft AGAIN' or 'BACK to aircraft'. This term is related to the field of aviation, specifically the study of aircraft. The crossword solution for this term is AERO, which is an abbreviation for aeronautics, the science of flight.