The temperate grassland biome that once covered much of the Great Plains and supports bison is the prairie.
Prairies are dominated by grasses, sedges, and flowering herbaceous plants rather than trees. In North America, rainfall generally increases from west to east, producing shortgrass, mixed-grass, and tallgrass prairie communities. Deep, fertile soils formed partly from dense root systems and the gradual accumulation of organic matter.
American bison were once a defining force in prairie ecology. Their grazing created a patchwork of differently sized grasses, while their movement, wallowing, and dung affected soil nutrients and helped other species. Fire worked alongside grazing to suppress woody plants and maintain open grassland.
The word prairie is sometimes used broadly for North American grasslands, while steppe is more commonly associated with dry grasslands in Eurasia and other regions. Savannas usually include scattered trees, and pampas refers especially to the temperate grasslands of South America. Those distinctions make prairie the canonical answer.