What is Transit gateway ?
AWS Transit Gateway connects VPCs and on-premises networks through a central hub. This simplifies your network and puts an end to complex peering relationships. It acts as a cloud router – each new connection is only made once
It is safe to say that Amazon Virtual Private Cloud is one of the most useful and central features of AWS. With the release of Transit Gateway we now have many options to connect to our VPCs.
You can learn about Transit Gateway here