Subdomain is a domain that is part of a larger domain. We also call it as a child domain. Subdomain can be used for many purposes. Either for product segmentation, staging and testing content, secure checkout and regional content. Therefore, it is not always necessary to register new domains, you can create a subdomain by using a domain you already own. For example:
google.com is a large domain for all Google services, Google created subdomains for product and services segmentation
a. play.google.com – a subdomain to handle mobile apps and ebook content.
b. adwords.google.com – a subdomain to handle advertisers bidding and keywords
c. drive.google.com – a subdomain to store cloud content and document
d. support.google.com – a subdomain to manage user question and product support
e. plus.google.com – a subdomain to handle social media contents
yahoo.com is a large domain for all Yahoo services, Yahoo created subdomains to manage multi-region content.
a. hk.yahoo.com – a subdomain to handle Hong Kong local contents
b. malaysia.yahoo.com – a subdomain to handle Malaysia region contents
c. sg.yahoo.com – a subdomain to handle Singapore local contents
d. uk.yahoo.com – a subdomain to handle UK region contents
e. ca.yahoo.com – a subdomain to handle Canada local contents
The benefit of subdomains
– unlimited subdomain, a large domain can create as many subdomains as needed
– save cost, there is no additional fee to create subdomains
– assign different IP for each subdomain. Therefore, it is not necessary to host all content in the same server.