To reduce confusion as to which frequency is being referenced in terms of a paired frequency set (duplex with separate input and output frequencies, as repeaters typically use, the downlink frequency refers to the frequency that the repeater is transmitting on. This is the frequency that is programmed into the user radio (HT, mobile, base) that you listen to the repeater on. This is the radio's receive frequency.
Confusion sometimes occurs when it is not known from which radio, the user's or the repeater's, that is being requested. Usually, it seems to get turned around when a repeater owner enters that data. Many repeater coordination councils request the repeater's frequencies in terms of the repeater's transmit and receive frequencies, which are opposite from the user radio's on a duplex system.
Repeaterbook enters and displays data from the perspective of the remote (user) radio.