QSFP-DD stands for Quad Small Form-factor Pluggable Double Density. It is a type of optical transceiver used in high-speed data communication and networking. The QSFP-DD can support data rates of up to 400 Gbps, making it suitable for data centers and enterprise networks that require high bandwidth. This transceiver is designed to fit into standard QSFP ports, allowing for easy upgrades and compatibility with existing infrastructure. The double density feature means it can accommodate more data channels in the same physical space, enhancing efficiency and performance in network systems.