An NNTP Client is a software application that allows users to access and interact with newsgroups over the Network News Transfer Protocol (NNTP). It enables users to read, post, and manage messages in various discussion forums, often organized by topics. These clients typically provide features like threading, search functions, and the ability to download attachments. Popular NNTP Clients include Mozilla Thunderbird and Pan, which help users stay connected to online communities and share information easily.