A blind beam-out was a method of using a transporter.
This method was used when normal means of acquiring a transporter lock on a subject were unsuccessful. A transport cycle was engaged within a designated area without knowing exactly who or what was present. This was usually done in an emergency situation where an immediate evacuation was required.
Seska performed a blind beam-out in 2371 when a subspace vacuole on an asteroid prevented her from getting a transporter lock on an away team composed of Chakotay, B'Elanna Torres, and Harry Kim. While Chakotay and Torres were returned to the USS Voyager, Kim's pattern was pulled into the vacuole. (VOY: "Emanations")