ExpressCard/54 is a standard for expansion cards used in laptops and other portable devices. It allows users to add various functionalities, such as additional USB ports, network connections, or storage options. The "54" in its name refers to the card's width, which is 54mm, making it slightly wider than the ExpressCard/34 standard. This interface supports both USB and PCI Express technologies, enabling high-speed data transfer. ExpressCard/54 slots are typically found in modern laptops, providing a convenient way to enhance device capabilities without needing to open the laptop or replace internal components.