why in the sql is used access <>0

In the query for to create th users list the sql is filtered also by the u.access <> 0;
but when an user have the access = 0?
and status=0 is when the user is blocked?

code example:
$result = pager_query("SELECT u.uid, u.name FROM {users} u WHERE u.status <> 0 AND u.access <> 0 AND LOWER(u.name) LIKE '%s%%' ORDER BY u.name ASC", $number, $element_override, NULL, drupal_strtolower($op));