Autorack, transporting cars on trains

Multiplexing, multiple signals combined into one

Seasoned trade line, strangers with bad credit using someone with good credit's credit card account

Piggybacking (security), occurs when an authorized person allows (intentionally or unintentionally) others to pass through a secure door, negating the purpose of an access control system such as keypad, pass card or biometric identification scanner

Piggy-back (transportation), something that is riding on the back of something else

Piggybacking (data transmission), a bi-directional data transmission technique in network layer

Piggyback plant, Tolmiea menziesii

Piggy-back (law), shareholder selling rights

Piggyback marketing, used to reduce risk, and more established companies can leverage the brand and market reach of a partner to help them very quickly pick up the credibility and awareness needed in new market segments.[1]

Piggybacking (internet access), obtaining wi-fi access by bringing one's own computer within the range of another subscriber's service

Piggyback registration, when owners of restricted stock in a public company are allowed to participate in a public offering underwritten by another party

Piggyback Interactive, a Europe-based company which mainly focuses on the creation and sale of video game strategy guides. They are the market leader in Europe, and have published guides for high-profile games such as Halo 2 and the Final Fantasy series.