What is this error?

PHP Notice: Undefined offset: 0 in /home/web/public_html/oc-content/themes/tatiana/functions.php on line 118

 
117 $cat = osc_search_category_id();
118 $cat = $cat[0];
119
120 $reg = osc_search_region();
121 $cit = osc_search_city();


Change:
$cat = $cat[0];
Into:
$cat = @$cat[0];