Lawns need not be, and have not always been, made up of grasses alone. Other plants for lawn-like usable garden areas are sedges, low herbs and wildflowers, moss lawns, and ground covers that can be walked upon.
Thousands of varieties of grasses and grasslike plants are used for lawns, each adapted to specific conditions of precipitation and irrigation, seasonal temperatures, and sun/shade tolerances. Plant hybridizers and botanists are constantly creating and finding improved varieties of the basic species and new ones, often more economical and environmentally sustainable by needing less water, fertilizer, pest and disease treatments, and maintenance. The three basic categories are cool season grasses, warm season grasses, and grass alternatives.
Read more, here.