A piggyback referred to the performance of two tasks simultaneously, in which the secondary task was carried as overhead to the primary one. This could 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. K'Vada was initially confused by the Human metaphor when Data used it. (TNG: "Unification II" )