A normal user, joe has the following record in the /etc/passwd file. What does the x indicate?

A normal user, joe has the following record in the /etc/passwd file. What does the x indicate?
joe:x:1021:1020:purchase_dept_user:/home/usr/joe:/bin/bash

• Password for user joe is locked
• Password for user joe is x
• joe has not yet set his password
• The encrypted password has been stored in the /etc/shadow file