Grand Teton National Park is the name of the national park just south of Yellowstone National Park.
Some people refer to the Grand Tetons, but, although there are three Teton mountains in the Teton Range, there is only one Grand Teton, and the name of the park is Grand Teton NP.
If you are traveling to Yellowstone NP, I highly recommend spending some time in Grand Teton NP too. There are many amazing views, and great potential for wildlife viewing and photography. I have photographed grizzly bears, black bears, bison, moose, elk, deer, wolves, coyotes, foxes, pine martens, beavers, bald eagles, ravens and crows, great blue herons, sandhill cranes, and more in Grand Teton NP.