What is the definition of source file?

Hi, I am having difficulty understanding something. 

I am learning about Master clip color correction. So the tutor duplicated a sequence, and he cuts it into several pieces and he named it 'multiple clip', and then he goes back into the source- lumetri color and if he changes it's lumetri it affetcs all the pieces in the time line. and he also gets red lines under the fx of all those pieces. 

now here where am lost. 

suppose in my priemer pro  the main  sequence's name is 'A'  and  duplicated one's name is 'Z', and I cut Z  into several pieces.... .  now  in my case which one is the master clip and which one is the source file? 

A= the original one= master clip and also source file?

Or

B= the duplicate one = master clip, not source file. 

and also I am not having any red lines under my fx  in time line panel. I want the red lines. What I have to do to get it?
thank you.