Technically, a router is any device which routes traffic at the IP layer (layer 3; based on IP addresses like 10.1.2.3 or fe80::abcd:1234), as opposed to some other later (e.g., a device which routes at layer 2 is a switch; a device which routes at layer 7 is a load balancer).
In colloquial usage, “router” usually refers to a home internet gateway, which is a device that does a few things:
serves as a masquerading gateway for your local network (allowing multiple devices inside your home to share a single IP address provided by your ISP)
serves as a traditional router for IPv6 if your ISP provides such access
contains an Ethernet switch allowing you to connect multiple Ethernet devices
often contains a WiFi access point, allowing you to connect WiFi devices and bridge them into your main network
has firewall/ACL systems to prevent the outside world from getting into your network
It usually does this by being a single box containing a small Linux or BSD computer running some custom software, dedicated WiFi and Ethernet chips, and some antennas. No magic there; you can do the same thing with any computer if you put enough elbow grease into it.
Also, all the devices in your home network (pc, tv, phone, thermostat, whatever) can talk to each other via broadcast. They just frequently yell out “I am here! See me!”. The router stops those broadcasts from going into your neighbour’s network or even the internet.
Technically, a router is any device which routes traffic at the IP layer (layer 3; based on IP addresses like 10.1.2.3 or fe80::abcd:1234), as opposed to some other later (e.g., a device which routes at layer 2 is a switch; a device which routes at layer 7 is a load balancer).
In colloquial usage, “router” usually refers to a home internet gateway, which is a device that does a few things:
It usually does this by being a single box containing a small Linux or BSD computer running some custom software, dedicated WiFi and Ethernet chips, and some antennas. No magic there; you can do the same thing with any computer if you put enough elbow grease into it.
Also, all the devices in your home network (pc, tv, phone, thermostat, whatever) can talk to each other via broadcast. They just frequently yell out “I am here! See me!”. The router stops those broadcasts from going into your neighbour’s network or even the internet.