Grass tennis shoes are a type of shoe used specifically on grass tennis courts. Grass shoes typically have more grip than a regular pair of tennis shoes as grass courts tend to be a more slippery surface. They also have flat soles so as to not damage the playing surface and a softer outsole since the court isn't as damaging to the shoe.
Some brands that manufacture and sell grass tennis shoes are Asics, Adidas, Lotto, New Balance, and Nike, among other brands.
Wimbledon is the only grand slam competition played on grass, making it the only grand slam competition that still requires grass tennis shoes. Slipping is much more prevalent on a grass court than any other surface, requiring a different type of shoe that is better equipped to keep an athlete from slipping or falling. Grass tennis shoes have little studs on the bottom of the shoe in order to improve traction and still protect the grass surface of the court.