FD-LTE uses frequency division duplex or 'paired spectrum'. The uplink is on band (say 10MHz wide at 2.200GHz) and the paired downlink is another 10MHz at a separated frequency (eg 2.400GHz) This is sometimes called 10+10. It is symmetric and uses two frequencies one up, one down.
TD-LTE is Time division. It has one frequency band, and switches between up and down in turn based on the runtime requirement