Captioned Telephone Service is a communication tool designed to assist individuals who are deaf or hard of hearing. It allows users to read real-time captions of what the other person is saying during a phone call. This service can be accessed through specialized phones or apps that display the text on a screen. The captions are generated by a communication assistant who listens to the conversation and types out the spoken words. This enables users to follow along easily, ensuring they can participate fully in conversations without missing important information.