A cable made up of glass threads that can be used to move information (e.g. a sound or a picture) very quickly from one place to another. This information travels through the fibers in the form of light.
An underwater Remotely Operated Vehicle (ROV) is a type of robot that helps us explore the underwater world. It has a tether (cable) which allows a human driver to sit on the shore, in a boat, or a submarine bubble and see what the robot 'sees' using a display, and move the robot about using remote controls.
Virtual Reality (VR) technology can help us experience something that isn't actually around us at the time. For example, you can experience being underwater without even getting wet by putting on a VR headset. Through the headset goggles you can watch a video of the underwater environment, and move your head around to see what is 'behind you' just as if you were under the water!