MySQL Group Replication is a new 'synchronous', multi-master, auto-everything replication plugin for MySQL introduced with MySQL 5.7. It is the perfect tool for small 3-20 machine MySQL clusters to gain high availability and high performance. It stands for high availability because the fault of replica don't stop the cluster. Failed nodes can rejoin the cluster and new nodes can be added in a fully automatic way - no DBA intervention required. Its high performance because multiple masters process writes, not just one like with MySQL Replication. Running applications on it is simple: no read-write splitting, no fiddling with eventual consistency and stale data. The cluster offers strong consistency (generalized snapshot isolation).
It is based on Group Communication principles, hence the name.