CNAME Records are domain name aliases. Often computers on the Internet have multiple functions such as Web Server, FTP Server, Chat Server, etc.. To mask this, CNAME Records can be used to give a single computer multiple names (aliases).
Sometimes companies register multiple domain names for their brand-names but still wish to maintain a single website. In such cases, a CNAME Record may be used to forward traffic to their actual website.
www.abc.in could be CNAME to www.abc.com.
The most popular use of the CNAME Record is to provide access to a Web Server using both the standard www.yourdomainname.com and yourdomainname.com (without the www). This is usually done by adding a CNAME Record for the www name pointing to the short name [while creating an A Record for the shorter name (without www)].
CNAME Records can also be used when a computer or service needs to be renamed, to temporarily allow access through both the old and new name.