Theoretically speaking, 2.4GHz is a frequency band that works in the ISM frequency band. The ISM band is an industrial, scientific and medical frequency band. Generally speaking, countries all over the world have reserved some wireless frequency bands for industrial, scientific research, and microwave medical applications. There is no need for a license to apply these frequency bands, only a certain transmit power (generally less than 1W) is required, and no interference to other frequency bands is required.
The regulations on ISM frequency bands in different countries are not uniform. And 2.4GHz is the common ISM frequency band of all countries. Wireless local area network (IEEE 802.11b/IEEE 802.11g), Bluetooth, ZigBee and other wireless networks can all work in the 2.4GHz frequency band.
The so-called 2.4G wireless technology has a frequency band between 2.405GHz-2.485GHz (science, medicine, agriculture). Referred to as 2.4G wireless technology.