piggyback

Piggyback is a versatile term used in several contexts. In its most literal sense, a piggyback refers to a person being carried on another's back or shoulders, usually by someone standing or kneeling to support the weight. The rider holds onto the carrier, and the arrangement is common in informal play, caregiving, and child-rearing, though it carries safety considerations.

In transportation, piggyback describes an intermodal freight operation in which road trailers or containers are loaded onto railroad flatcars for part of their journey. The reverse transfer is called rail-to-truck or truck trailer on flatcar. This approach combines the flexibility of road transport with the energy efficiency of rail.

In telecommunications and security, piggybacking can refer to unauthorized access of a network by using another user's connection without permission. It can also describe a legitimate method of extending a network where one device temporarily communicates through another's link; however, it is often used to describe the former in informal contexts.

Metaphorically, to piggyback means to exploit someone else's work, status, or idea to further one's own goals. In business, science, and media, this usage notes reliance on others' investments, reputation, or data to gain advantage.

Etymology and usage vary; the exact origin is unclear, but the modern sense generally derives from the image of a person riding on another's back, with variants such as "piggy-back" and "pick-a-back" appearing in historical usage.