GoKawiilAs the name implies, a dual-band router broadcasts Wi-Fi on two radio frequencies at the same time: 2.4GHz and 5.0GHz. It's a simple explanation for a profoundly useful feature, especially when the average US household burns through over 700GB of data a month. With as much data as 4K streaming and gaming consume, imagine every device in the house depending on a single lane of traffic. Dual-band routers help relieve those potential bottlenecks, though each band has its own weakness and strength.
The 2.4GHz band has more reach and penetrates walls or other household obstructions more effectively. It's useful for devices in distant rooms or for less demanding smart home accessories. However, it's also the slower of the two and tends to be more crowded, with most devices defaulting to a 2.4GHz connection. The 5.0GHz band offers more wireless capacity and faster speeds, but it suffers from significant range limitations and doesn't travel through dense obstacles very well.
In most cases, a dual-band router automatically connects compatible devices to the best frequency band. Even so, when connecting a new device, you may see different network names, like "Home WiFi," "ATTnet" or something similar. Some routers display the frequency bands prominently in the list of available networks, and others don't. It all depends on the router.