What is the difference between threads connected and threads running
Threads connected means the total number of client processes (threads) connected to the database server. This includes the count for threads running.

Thread running means the total number of client processes (threads) currently executing on the database server. The server is holding these connections while the client is waiting for a reply. These thread may be consuming IO/CPU, while others may do nothing while waiting for a table lock to be released. When the database is finished executing the thread, the client gets a reply, and the thread is changed from status "running" to "connected".