Google Chat is now an integrated part of the Google+ feature set, allowing you to converse with members of your circles.
If you have logged into Google+ in the past day or so, you may have seen a bubble notification that you can now enable Google Chat on your Google+ page. If you ignored it or closed it without paying much attention, like I did, you can still enable it by clicking the button in the left navigation bar.
When you do, the Google+ members in your circle, assuming they have turned on the Chat function also, will be available for a chat conversation.
For some this is a good thing - chatting for many is a preferred form of communication. For some, like me, it is the worst way to communicate. The only reason it is on now is so I could show you what it looks like.