What is frequency coordination?

Basically, it is a form of voluntary participation in an organized program intended to keep interference between repeaters and their users to a minimum. To do this, repeater sponsors work with their local frequency coordinator (FC) who maintains a database of repeater frequencies in active use (as well as new repeaters which are under construction but may not yet be in operation). The FC recommends repeater operating frequencies (and perhaps other technical details) which will, hopefully, be compatible with other existing repeaters.