The term 'BARS UNDER BAR CARS' can be summarized as follows: the first word, 'BARS, ' refers to metal bars that are used to construct railway tracks, and the second word, 'RAILS, ' refers to the tracks themselves. The phrase is a metaphor for the way in which railway tracks are laid down, with the metal bars forming the foundation of the track and the cars running along them. This phrase is often used to describe the construction of railway lines, as well as the operation of trains on them.