Hi Hadi, Welcome to Webmaster World!
If one registers a new (or previously registered, but expired) domain, the minimum registration period, AFAIK, is one year.
There are circumstances, however, under which one could become a new registrant of a domain with less than one year before the expiration date.
(1.) I could agree to sell or give you a domain name that I have, that, say, expires in 3 months, and make you the registrant.
I could retain that domain in my account, or with many registrars, you could open your own account with that same registrar, and I could "push" the domain into your account. This would not be a "transfer" -- which would add 1 year to the registration.
(2.) If I purchased a domain name at any of the auctions in the so-called "secondary market", sometimes that domain is moved to a registrar account that I then take control of. While many auctions include a year of registration, many are for less than a year.
In either of the above scenarios, if someone did a whois lookup on that domain, they would see me as the "new registrant", and a domain expiration period of less than one year.