Understand hostname and /etc/hosts

In /etc/hostname, I have myname.

In /etc/hosts, I have :

127.0.0.1   localhost.localdomain   localhost myname
::1     localhost.localdomain   localhost myname

I have a vague understanding of what really is a hostname and what it is used for.

These more precise questions could help me to understand it better:

1. 
   

   What really is my hostname in the example above? myname or something else? If I had instead myname.domain.com in /etc/hostname, what would be my real hostname then?

   
   


2. 
   

   In the example, the command hostname returns myname, whereas the command hostname -f returns localhost.localdomain. I had in mind that /etc/hosts was only a mapping between names and ip addresses. It seems to serve another function here. What is a fqdn and what is it used for? How is it retrieved? Why is it localhost.localdomain?

   
   


3. 
   

   If I had instead myname.domain.com in /etc/hostname, hostname -f would return myname.domain.com. Why?

   
   


4. 
   

   Why aren't fqdn ending with a dot in these files?

   
   


5. 
   

   Are hostname -d and dnsmydomain equivalent?

   
   


6. 
   

   In what context can I use my hostname (myname) and when do I have to use my fqdn (localhost.localdomain)?