Wikipedia says a "tussock" is also known as "bunch grass"
Also commonly called tussock grass, bunch grasses are any grass that grows in clumps or tufts, rather than forming a sod or mat, and does not spread by stolons or rhizomes. As perennial plants, they live more than one season. With long roots that may reach two meters into the soil, bunch grasses can find water where other plants wither.
Bunch grasses occur in almost any habitat where grasses are found, from deserts, swamplands, savannas, forests and tundra.
Now if you'll view the below animation you'll notice the ground is littered with clumps of grass - these are tussocks.