From The RadioReference Wiki
The Output Frequency is the output of a Repeater. This is the frequency that you would (in most cases) program in your scanner to monitor a channel.
The output frequency is the only frequency specified in Trunking systems and is designated as the Frequency column on conventional systems.
Repeaters use both an input and an output frequency. The input and output are separated by an Offset which in many bands is standardized.
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