The term Sub domain refers to the part of domain name. It basically organises and navigates to different sections of the webiste. On the other hand, subdirectory is the pathway within the website. Subdirectories are the level within the domain's hierarchy. The basic difference between the subdomain and subdirectory is the way to organise the content on the website. The difference between them affects the website's ability to gather and rank keywords. Both are different concept.
