PHP short tags refer to the alternative way of writing php tags in a web script. i.e. <?= [function/variable]  ?>instead of <? php  echo [function/variable] ?>
Today while working on one my projects, I found that I needed to turn on PHP SHORT TAGS in the php.ini to make it work properly. The project uses codeigniter framework and the previous developer used php short tags in his code which was not setup on my localhost. So I enabled it by editing the php.ini file and setting the short_open_tag variable to on and then restarted the apache server and it worked.