A transmission from one station to another station in circumstances where two-way communication cannot be established but where it is believed that the called station is able to receive the transmission.
Source: ICAO Doc 4444 PANS-ATM
Blind transmissions can be used when providing air traffic service (ATS) in case of radio communication failure. When the the controller (or FIS officer) expects that the loss of communication is one-way (i.e. the pilot can hear messages but is unable to respond), they may provide information (e.g. about an aerodrome, weather, airspace restrictions, etc.) or in some circumstances issue clearances and instructions.
Pilots can use blind transmissions in various situations, e.g.:
at aerodromes where no ATS is provided, to inform other traffic of their intentions.
while cruising through airspace where no air traffic service is provided, to inform other traffic of e.g. their position, level, direction of flight, intentions, etc.
in case of receiver failure, in order to inform ATS units and other traffic of their intentions. This procedure is defined for some ICAO regions (MID/ASIA and PAC) in ICAO Doc 7030 (Regional supplementary procedures).
as a follow-up procedure in case communication with the appropriate ground station could not be established.