Thunderbolt (previously called Light Peak) is a new peripheral-connection technology, developed by with collaboration from Apple, that combines data, video, audio, and power in a single connection. Based on the PCI Express and DisplayPort architectures, Thunderbolt allows for high-speed connection of peripherals such as hard drives, RAID arrays, video-capture solutions, and network interfaces, and it can transmit high-definition video using the DisplayPort protocol. Each Thunderbolt port also provides up to 10 Watts of power to connected peripherals.

Light Peak was simply Intel's codename for Thunderbolt while the technology was under development--they're names for the exact same technology. One thing to note, however, is that although Thunderbolt is designed to allow the use of either electrical or optical connections, Apple's current implementation uses only electrical circuitry, which allows the port to carry power, as well. (Intel both for this advantage and because of the lower cost. Optical versions will likely be used only when cables longer than three meters are needed.)