A domain push is the transfer of a domain between two parties who use the same registrar. It is the transfer of a domain within the same registrar and may often be referred to as an “internal account change.” Many registrars have a system in place through which a domain can be moved from one account to another at the same registrar. This process is instantaneous and often saves time while avoiding related registrar transfer fees. Yes, it is free.
For example, suppose the domain you want is registered with Godaddy and you have an account there. Then you can request the domain push via Godaddy in the buyer’s dashboard, and you can receive the domain immediately from the buyer’s domain push. It can save you time and the transfer fee.
Please note that some registrars do not have a push system in place, especially those that have sign-up fees.