The sybmol with angel bracket and percentage sign like this one "<% %>" what is the meaning of this symbol and where it is used

<input type="hidden" name="item_number_<%= idx %>" value="<%= items[i].get("item_number") %>" /> I downloda the template containing html css and javascript language, where i found the above code of line what is the meaning of this symbol "<% some code %>".Please anybody guide me.