IEEE 802.11
Data communication is done in the 2.4 GHz band and the 5 GHz band.  The 2.4 GHz band is a general use band.  Microwave ovens and Bluetooth are among the things that emit radio waves in this band. The 2.4 GHz band has the problem that there are only very few channels that can be used at the same time, without the signals interfering. There are three usable channels there. When more than three networks operate in the same place, signals still get to the user correctly, but interference slows them.