What does it mean when MySQL is in the state “Sending data”?

Question

What does it mean if the Mysql query:

SHOW PROCESSLIST;

returns \"Sending data\" in the State column?

I imagine it means the quer

Answer 1

In this state:

The thread is reading and processing rows for a SELECT statement, and sending data to the client.

Because operations occurring during this this state tend to perform large amounts of disk access (reads).

That's why it takes more time to complete and so is the longest-running state over the lifetime of a given query.