Thunderbolt cables and adapters, both Thunderbolt 1- and 2 cables and the new Thunderbolt 3 cables with USB-C connectors.
Thunderbolt is a connection technology for transmitting both image and data signals in one and the same cable. Over time, the Thunderbolt standard has evolved from using connectors of the same type as the Mini Displayport (Thunderbolt 1- and 2) to now with USB-C connectors (Thunderbolt 3).
The great advantage of Thunderbolt connections is that you can connect a Thunderbolt docking station/hub or monitor with just a single cable. Eg. for fast connection at the desktop workplace for the laptop, where the fixed connections to peripheral devices (monitor, keyboard, network, etc.) are connected to the dock. This is the same as for USB-C hubs and docking stations.
Thunderbolt is the name of a high-speed cable technology, originally developed by Apple and Intel, as a competitor to USB 3.0 (now USB 3.2). During the development phase, the standard was names Light Peak, as it was originally intended for an optical cable type. Closer to launch, the name was changed to Thunderbolt and the cable type to ordinary data cables, as copper technology was eventually good enough to support the high speeds. Thunderbolt cables are designed to connect electronic devices to each other for high-speed data transfer, in the form of both an image signal such as Displayport video, and a PCI data signals in the same cable. This meaning that you can connect everything from external hard drives to monitors via Thunderbolt if they support it.
The Thunderbolt cable standard is designed to deliver a high bandwidth and extremely high speed from the start of 10 Gbps. per second, and has potential at 100 Gbps over time via optical cables, but e.g. at "just" 10 Gbit / sec. you can transfer data amount equal to a full-length Blu-ray movie in just 30 seconds. The technology used also allows for smaller plugs and longer cable runs than for example traditional USB cables. Thunderbolt connections are backwards compatible with the Displayport 1.2 standard.