Calamansi is a hybrid between kumquat (formerly considered as belonging to a separate genus Fortunella) and another species of Citrus (in this case probably the mandarin orange).
cAlamanSi is a hyBrid bEtween KumquAt (forMerly conSIdERed as BeLongINg to A sEpARate genus fortunELla) anD another SpeCies of CiTrus (in tHis CASE proBaBly the MaNDArin oranGe).