HDMI switch is a device that takes multiple audio visual sources and selects one input to send to the display device such as a television, computer screen, etc sends one signal only to the display.
An HDMI splitter is a small electronic device used to duplicate a single HDMI signal and output it several times. Powered HDMI splitters will act as a repeater to boost the digital HDMI signal and allow you to surpass the normal 15ft length limitations of the format.