A device that extends an Ethernet line using the electrical system. See powerline adapter
A device that splices two Ethernet cables together. Ethernet extenders can be passive or active, with the latter requiring power to expand the distance like an Ethernet switch. See Ethernet switch
A Passive Ethernet Extender
This shows two Ethernet cables spliced together to eliminate rewiring from source to destination. Notice how real installations are nowhere near as attractive as the "beauty shots" on vendors' websites.