How are these types of variables called "TMPL_VAR NAME = JAVAURL" and how are they used?

I'm working on a system made in perl, javascript and html, but I came across this variable:

<TMPL_VAR NAME=JAVAURL>

  

<script language="javascript" src="<TMPL_VAR NAME=JAVAURL>/Functions.js"></script>

I had never used them, could someone help me to give me an idea of how these types of variables are used?

I will thank you!