Why using the symbol "$" in Angular : <p><a href="https://i.stack.imgur.com/p7705.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/p7705.png" alt="enter image description here"></a></p>

<p>Based on the picture with the white selection.</p>

<p>I don't understand why you need to use the symbol "$". (<a href="https://www.twilio.com/blog/prevent-memory-leaks-angular-observable-ngondestroy" rel="nofollow noreferrer">https://www.twilio.com/blog/prevent-memory-leaks-angular-observable-ngondestroy</a>)</p>

<p>What is the purpose to use a symbol "$"?
What benefit is it to use it?</p>

<p>Thank you!</p>
