The Large Windows option facilitates the advertisements of windows larger than 2**16. This is useful in high bandwidth long delay networks such as satellite links. It defines an implicit scale factor, which is used to scale up the window size value found in a received TCP segment to obtain the true window size. With this scaling, receive window advertisements can go up to 1 GB.
This Large Window option is negotiated when establishing the connection.
For more information, see Large Windows.