Refer to figure.
Blind transmission. 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.

ICAO Doc 9432 - Manual of Radiotelephony
9.5 AIRCRAFT COMMUNICATIONS FAILURE

9.5.1 When an aircraft station fails to establish contact with the aeronautical station on the designated frequency, it shall attempt to establish contact on another frequency appropriate to the route. If this attempt fails, the aircraft shall attempt to establish communication with other aircraft or other aeronautical stations on frequencies appropriate to the route.

9.5.2 If the attempts specified under 9.5.1 fail, the aircraft shall transmit its message twice on the designated frequency(ies), preceded by the phrase “TRANSMITTING BLIND” and, if necessary, include the addressee(s) for which the message is intended.

When there is a radio communication failure or discrepancy, the pilot may choose to transmit blind to the ATC. This means the pilot will transmit messages even though they cannot hear the ATC's reply, because there is a possibility that the ATC may be able to hear the aircraft transmission. Similarly, the ATC may also transmit blind to an aircraft when there is no radio contact, but it is believed that the aircraft might receive the message.