체코 공화국 -- except they rarely use the long form in conversation. Some people have been pushing 체키아 (Czechia) but it hasn't caught on yet outside of some reports. Then there's the Czech name, rendered 체스코 공화국 on Wikipedia (Česká republika, pronounced "Chéskă" -- the feminine of the adjective český to agree with republika, all together synonymous with noun form Česko). Trust me; I triple checked ;-) . . .