Voice Over LTE (Long Term Evolution)
A standard allowing voice calls to be placed over an LTE network.
VoLTE also updates voice connections to use a more more modern packet-switching technology, instead of old, inefficient circuit switching.
See: Packet Switching
See: Circuit Switching
Most LTE networks worldwide were launched initially supporting only data service. A stop-gap technology called CSFB allowed phones to use LTE for data and 2G or 3G networks for voice.
VoLTE allowed LTE (4G) networks to completely replace 2G and 3G networks. It also eliminated the need for CSFB.