What is {{}} in html code example

Example 1: # in html

# in CSS means your looking at an ID so 
<div class="ExampleClass" id="ExampleID"></div>

#ExampleID would reference the ID
.ExampleClass would reference the class

Example 2: html

Hypertext Markup Language is the standard markup language for documents
designed to be displayed in a web browser.

It can be assisted by technologies such as Cascading Style Sheets and
scripting languages such as JavaScript.