Wikipedia defines a fishing gimbal as - In saltwater fishing, it is also a device used for landing large fish. When fishing with a large rod, a gimbal transfers the weight of the rod from the arms and wrists of the angler to the hip or waist, effectively allowing the angler to concentrate on leveraging the rod instead.
Inside the gimbal there is usually a horizontal pin that the fishing rod locks into, allowing rotation of the rod in one plane only, up and down.
During one of my escapades to a tackle shop in Ipoh, I saw an aluminum gimbal which looked quite good. I am not sure on the functionality or the comfortability of using it, but it sure looks good.