A false ceiling creates a layer of insulation between the main ceiling and the room. This buffer layer traps some of the heat coming from the roof through the main ceiling thus reducing the transfer of this heat to the room. This helps to keep the room cool
any ceiling that is suspended below the original ceiling usually to conceal an ugly, or too high ceiling or to install flourescents with translucent panels to give the effect of the entire ceiling being lit up. lots of reasons and methods but basically is just a 2nd ceiling concealing the original.