The phrase "reply button" refers to a clickable option or symbol on a computer or mobile device that allows you to respond to a message or comment. Full definition
The «classic» version had a quick reply button — a little dialog box popped up — letting you reply in seconds. (lawyerist.com)
Users who view your update can also reply to that update via reply button. (gogi.in)
funny how when I clicked on the Disqus reply button on the Disqus alert email for this thread / post, it actually took me to GoodEreader story on the Amazon / imdb boards disbandments.. (goodereader.com)