An underlined frequency in the Frequency column means that there is a broadcast on this frequency currently on air.
Note that for station rows, there may be several frequencies in the Frequency column, some underlined and some not, according to what broadcasts are currently on air for this station.
If, additionally, an underlined frequency is displayed in the gray color, it means that the frequency is currently above the Maximum Usable Frequency for the broadcast transmitter location.
See also
See what stations, broadcasts and programs are currently on air
See what stations and broadcasts have inactive status
About viewing schedules in the Stations view
About estimating propagation
Stations tree table, Frequency column