Fields in USR02 table ?

What is the significance of TRDAT (Last logon date) column of USR02 table ? For any user if these column shows 00/00/0000 does it mean that this user has <b>"never logged in to that system"</b> after creation of his id ?

Whether any lock/unlock,password reset etc activities can reset TRDAT value to 00/00/0000 ?