What is the different between GRE and Tunnel?
GRE is a tunneling protocol. It encapsulates other protocols,(AKA IP,IPV6,IPX) into IP protocols. GRE makes the point-to-point link for you. One thing to remember,GRE doesn't encrypt anything for you.
GRE is a tunnel. There are many types of tunnels. For example there are also MPLS Traffic Engineering Tunnels.
Steve Lyons - Cisco