The FLUSH statement can be used to clean or reload various internal caches, flush tables, or acquire locks. Flush means reset.
MySQL will clear the host cache when you use FLUSH HOSTS, which effectively implies MySQL’s record of which hosts are now or have recently connected is reset, allowing you to connect to those hosts again.
In other words, The command uses host cache tables; if the maximum number of connections for a certain host has been reached, mysql server will be unable to initiate new connections. Flushing host tables restarts the process and re-allows connections to specific HOSTs.
MySQL> FLUSH HOSTS;