A lower Web page in a website that can be located using the exact domain name followed by a slash symbol and text. As a rule of thumb sub pages should never be more than three clicks away from the home page. A flat website architecture is important for usability and also prevents the unnecessary dilution of link juice as it travels from the home page to the sub pages.
For a website with many pages, creating subpages allows developers to limit the number of pages that apear in the main navigation. You can also have visitors navigate through other pages of a site to find related content.
Page vs Sub Page
Sub pages are the same as other pages except they are used to organize information. A sub page makes it easier for website visitors to access information and navigate the site. These pages are used on most websites and are no different than standard pages. They only make organizing information easier.
For example: www.bluefountainmedia.com/ecommerce-design