What is the convert.common.temperature action?

[khoi-thinh]

Hi,

I came across this sample and found it very useful to help understand how to create card to display address link and image.

There's one thing that I'm not sure i understand. That's under Action and Parameters section of Convert Fahrenheit and Celsius, i noticed there was this text : convert.common.temperature

Can someone explain why we need this? And how can i know which is the right action to put in?
I understand there's $temparature parameter but what about convert.common? I didn't see such a thing in Intents, Entities or Fulfilments.