Dual-Band Wi-Fi is a form of broadband offered by most providers nowadays. Dual Wi-Fi frequency has dual-band for 2.4GHz and 5.0 GHz. The device you're using can connect to either the 2.4GHz or 5GHz band depending on your needs.
A wireless transmission at 2.4 GHz provides internet to a larger area but sacrifices speed, while 5 GHz provides faster speeds to a smaller area.