An advertising postcard is a commercially produced, rectangular piece of stiff paper (typically 3.5 x 5.5 inches) specifically designed to carry promotional messages for products or services, either mailed or distributed directly. Its origins trace back to 18th-century "trade cards," which evolved into widely used advertising postcards by the late 19th century by prominent companies like Colgate & Palmolive, and even for propaganda. However, their popularity waned in the 1920s with the advent of commercial radio, only to experience a significant resurgence in the 1990s as part of strategies targeting mobile and 'hard-to-reach' youth markets.

These postcards are distributed either through direct mail, sometimes in unique die-cut shapes allowed by postal authorities, or are freely available on display stands in high-traffic areas like shopping malls and university campuses. Beyond their commercial utility, advertising postcards have been immensely popular with collectors since the 18th century, even inspiring a "mania" in the 19th century, and are now studied by scholars for insights into the emergent commercialization of consumption.