tour de force /ˌtʊə də ˈfɔːs $ ˌtʊr də ˈfɔːrs/ BrE AmE noun [singular] written
[ Date: 1800-1900 ; Language: French ; Origin: 'impressive act of strength' ]
something that is done very skilfully and successfully, and is very impressive:
His speech to the Democratic Convention was a tour de force.