Splitters, switchers. Audio video switches, select what is shown on each monitor, etc. Switchers are usually needed when you need to chose a video source individually at each monitor or if you are using multiple devices going to one monitor.
Do you want to control what is displayed on each monitor? Maybe one person wants to watch a DVD and the other kid wants to play video games.You need these switchers and splitters. Controls the source to each monitor, allows multiple sources.