Communications frequency
A communication frequency or hailing frequency was a frequency in which audio or visual communications were conducted. 

There were many subspace frequencies over which hails were sent. Most of the major powers, such as the United Federation of Planets and the Dominion, had their own frequencies and protocols for sending messages such as distress calls, but there were also general frequencies. ()

When contacting a starship or space station the normal command was "open hailing frequencies". (; , et al.)

Many types of atmospheric disturbance and certain elements or compounds would prevent hailing signals from reaching their destination. () 

Jamming of hailing frequencies was a common technique used for purposes such as disrupting enemy communication in battle and preventing vessels from emitting a distress call. Most jamming techniques did not prevent the jamming party from sending out its own hails. Of particular note was the Breen method of sending out a rotating electromagnetic pulse. ()

List of frequencies 
 Subspace frequency 3 ()
 384.2 gigahertz ()
 Comm frequency epsilon-2 ()
 Starfleet frequency 1486 was the comm channel the  tied into to listen to the fleet's battle against the Borg in 2373. ()
 Top space frequency of 39 ()

Types of frequencies 
 Radio frequency
 Theta band frequency
 Vulcan band frequency
Mathematics
Communications technology