Difference between subdomains `WWW` and `m`

What's the difference between these two subdomains WWW and m?
For instance, WWW.medium.com and m.medium.com

In my country, WWW.medium.com is blocked, but when I try using m.medium.com instead, It works well. So I want to know what's the difference between them? Can they have different content?

PS: I have searched about that, but haven't found anything related
Thanks in advance.