Rich Communication Services
A global industry standard for phone messaging and multimedia communication. It replaces SMS and MMS with a new platform that more modern and flexible.
Just as VoLTE is a more modern standard for voice calls, RCS is the equivalent update for messaging and media, including chat, video, and file sharing. Both VoLTE and RCS update the industry standards for mobile to be fully IP-based (like the Internet), which is one of the key goals of 4G mobile network technology.
As a replacement for SMS/MMS, RCS includes modern chat features like presence, so you can see when the other party is offline, when they are typing, and whether they received messaged you have sent.
The RCS standard also supports functions such as file sharing and live video sharing.
RCS is intended to be built into phones as part of the default messaging app/experience, and is planned to be as ubiquitous and interoperable as SMS.
As of 2016, RCS has little adoption, but several major US carriers have promised to launch it, and Google has committed to offering the necessary phone software for Android.