VHF stands for Very High Frequency and UHF stands for Ultra High Frequency.
The difference between these two types
of wireless microphones is the region of the FM band (audio spectrum) in which each system is designed to operate.
Both regions are reserved by law and separated from other frequency
spectrums. Similarly other frequencies are designated for various radio wave transmitting devices, such as walkie-talkies or FM hearing assistance.
By choosing equipment within the VHF and UHF bands you can generally avoid interference from other types of wireless devices. In the
frequency range of UHF the clarity of transmission is better than VHF because the separation from other transmission sources is better - there is also a wider spectrum to choose from. The tradeoff is that UHF generally costs a bit more than VHF.
In particular, wireless VHF microphones operate on frequencies below approximately 300 MHz. In the U.S., most such systems operate somewhere between roughly 170 MHz and 216 MHz, with lower frequencies available for certain specialized applications.
UHF picks up where VHF leaves off. In wireless microphones, UHF systems operate between approximately 450 MHz and 952 MHz. In the U.S., most such systems operate somewhere between roughly 524 MHz and 806 MHz, or 944 MHz and 952 MHz.