A piggyback refers to a condition where one thing is done as a part of something else, in which the secondary task is carried as overhead to the primary one. This can occur in regards to a computer system piggyback.

Data, in 2368, with the assistance of Captain K'Vada, accessed the Romulan Central Information Net to send a transmission to the USS Enterprise-D, piggybacking it on Romulan transmissions. (TNG: "Unification II")