ATA stands for an analog telephone adaptor. It’s a device used to bridge standard telephones and PBXs to a network so that calls travel over the Internet instead of direct over copper wire.
There are several different kinds of ATAs. All of them are a physical bridge between a phone and a network device. Some types some perform analog-to-digital conversion and connect directly to a VoIP (Voice over Internet Protocol) server. Other types of ATAs use software, rather than hardware to perform the tasks.