What is WIFI channel in router device? May i know the function of WIFI channel in router device?

Home and small business routers that incorporate a WiFi access point (most do these days) allow you to set the "channel" that the access point uses. For normal WiFi devices there are 12 channels, the default of which is usually 6. That said, since 6 is the default, the more traffic on a specific channel there is (and accessible, but non-connected access points will affect this), the slower your speed and throughput will be. If that seems to be an issue for you, you can go into the router/AP setup (web) menu and change the channel. You can experiment until you find one that works best for you. The devices that connect to the AP (access point) will adapt automatically.

All Wi-Fi network equipment including client devices and broadband routers communicate over specific wireless channels