In domains are used in website for displaying contents.In this concept we see the difference between domain and subdomains .Domain is actual website in server.
Subdomain:
Subdomain is a sub folder in web server .for example Blogspot is a subdomain.In subdomains are act as a subfolder of website.In subdirectory is a different because subdirectory is used in ftp.
For a clear example:
Domain:www.maxicsolutions.com
Subdomain:maxicsolutions.forum.com
Subdirectory:www.maxicsolutions.com/home
