RCS, or Rich Communication Services, is a messaging protocol that allows for the transmission of richer content, such as high-resolution images and videos, over standard SMS networks. Apple has yet to adopt RCS, which has led to some frustration among users who want to be able to send these types of messages to their iPhone-using friends and family.
There are several benefits to using RCS over SMS, including the ability to send larger files, see when your messages have been read, and create group chats with more than 10 people. RCS also supports end-to-end encryption, which means that your messages are protected from being intercepted by third parties.