What do the columns in SYS.USER$ represent?
Test cases below show:


CTIME is the date the user was created.
LTIME is the date the user was last locked. (Note that it doesn't get NULLed when you unlock the user).
PTIME is the date the password was last changed.
LCOUNT is the number of failed logins.


Here's the test code:

SQL&gt; create user philtest identified by philtest;

User created.

SQL&gt; alter session set nls_date_format='HH24:MI:SS DD/MM/YYYY';

Session altered.

SQL&gt; select ctime,ltime,ptime from user$ where name = 'PHILTEST';

CTIME               LTIME               PTIME
------------------- ------------------- -------------------
14:21:51 26/04/2012                     14:21:51 26/04/2012

SQL&gt; alter user philtest account lock;

User altered.

SQL&gt; select ctime,ltime,ptime from user$ where name = 'PHILTEST';

CTIME               LTIME               PTIME
------------------- ------------------- -------------------
14:21:51 26/04/2012 14:23:15 26/04/2012 14:21:51 26/04/2012

SQL&gt; alter user philtest identified by foofoo;

User altered.

SQL&gt; select ctime,ltime,ptime from user$ where name = 'PHILTEST';

CTIME               LTIME               PTIME
------------------- ------------------- -------------------
14:21:51 26/04/2012 14:23:15 26/04/2012 14:27:47 26/04/2012

SQL&gt; 


This isn't documented in the Oracle docs, as it's an internal data dictionary view. However, the DBA_%/ALL_%/USER_% views that sit on top of the SYS.% views are documented here.

I often find that doing a DESCribe on one of the DBA_% views gives a good indication of what the underlying columns represent. The DBA_% views are often commented too.