The user just logged out.
Note that when this hook is invoked, the changes have not yet been written to the database, because a database transaction is still in progress. The transaction is not finalized until the save operation is entirely completed and user_save() goes out of scope. You should not rely on data in the database at this time as it is not updated yet. You should also note that any write/update database queries executed from this hook are also not committed immediately. Check user_save() and db_transaction() for more info.
$account: The user object on which the operation was just performed.
Note: this list is generated by pattern matching, so it may include some functions that are not actually implementations of this hook.
function hook_user_logout($account) {
db_insert('logouts')
->fields(array(
'uid' => $account->uid,
'time' => time(),
))
->execute();
}