The Collaborative International Dictionary of English v.0.48:

Gre \Gre\, n.
   See Gree, a step. [Obs.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Gre \Gre\, n.
   See Gree, good will. [Obs.]
   [1913 Webster]

The Free On-line Dictionary of Computing (19 January 2023):

Generic Routing Encapsulation
GRE

    (GRE) A protocol which allows an
   arbitrary network protocol A to be transmitted over any other
   arbitrary network protocol B, by encapsulating the packets
   of A within GRE packets, which in turn are contained within
   packets of B.

   Defined in RFC 1701 and RFC 1702 (GRE over IP).

   (1998-07-19)