Mesh WiFi systems let you effectively add additional compatible WiFi satellites that act as routers, which means better and more consistent signal strength, all on which is treated as a single local network. In many respects, WiFi extenders are old tech when stacked next to their successor: the mesh WiFi system.
These networking devices are designed to mirror and extend an existing WiFi network. If your internet is slow, you can always make use of a WiFi extender, booster or alternatives. WiFi extenders are handy for larger homes that want to expand the signal of a WiFi router to far-reaching parts of the home or outside. They sit next to each other, they look pretty identical, and they both help you. Technically, a modem can connect directly to a networking switch, but this would eliminate wireless connectivity in the home. The router and the modem are two of the easiest devices to get confused. For homes that want as many Ethernet connections as possible, a networking switch can connect to a router to further delineate local network traffic, whereby the router can mainly tackle wireless connections, and the switch takes care of wired connections.
There are a couple of other networking gadgets in the home that are designed to liaise with a modem, a router, or a modem-router.