<?php
$mystring = "seminar_juridic_sergiu_22_01_2013_2";
//get juridic out of the string if it exists
$uline_pos = strpos($mystring,'_');
$str_no_prefix=substr($mystring,$length+1);
$uline_pos = strpos($str_no_prefix,'_');
$final_string = substr($str_no_prefix,0,$uline_pos);
echo $final_string;