How does 'access content' permission string works?
Read: https://api.drupal.org/api/drupal/modules%21system%21system.api.php/function/hook_menu/7


'access content' means 'Node: View published content' on permission list. Check this link for list of permissions provided by node module: https://api.drupal.org/api/drupal/modules%21node%21node.module/function/node_permission/7
'access content' will be passed as a first argument to user_access() which is default access callback for new menu items. You can change default access callback like this:

function custom_menu_menu(){
  $items = array();
  $items ['status'] = array(
    'title' =&gt; 'My Status',
    'menu_name' =&gt; 'main_menu'
    'page callback' =&gt; 'status_page',
    'access callback' =&gt; 'custom_menu_access_callback',
    'access arguments' =&gt; array('access content', 'something else'),
  );
  return $items;
}

function custom_menu_access_callback($arg1, $arg2) {
  // arg1: access content
  // arg2: something else
  // if this function returns TRUE user will get access to page callback
  // if this function returns FALSE user won't get access to page callback
}