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 uplink frequency refers to the frequency that the repeater is receiving on. This is the frequency that is programmed into the user radio (HT, mobile, base) that you transmit to the repeater on. This is the radio's transmit frequency. Some radios are equipeed with automatic offset and the user does not actually program in a transmit frequency, but simply indicates if the repeater is a positive (+) or negative (-) shift.
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.