Archaic term for a person from China, used in historical contexts. The word 唐土 (もろこし) itself is an old name for China.
In old Japan, people who came from China were called 'morokoshibito'.
From 唐土 (もろこし, an old name for China) + 人 (びと, person). The exact historical derivation of 唐土 is uncertain, but it was used in classical Japanese to refer to China.