An HDMI splitter takes a signal from one source and sends it to two separate displays. A switcher, on the other hand, connects several devices to one display.
A splitter is appropriate for connecting a single media source, such as a satellite receiver, DVD player or video game console, to televisions in different rooms. Because each screen will display the same content, a single presentation can be broadcast to multiple screens in an auditorium using a splitter. If, however, a single screen is to serve as the display for several components, an HDMI switcher is necessary to connect them simultaneously.