a giant South American grass (Cortaderia selloana) cultivated for use as an ornamental and for its large, plumelike, silvery or pinkish panicles used in bouquets
See pampas grass in American Heritage Dictionary 4
(pămˈpəs)
noun
A grass (Cortaderia selloana) of southern South America, having silvery plumes and growing in large clumps more than three meters (ten feet) tall.