The evidence of women being forced into sexual slavery, a system known as "comfort women," by Japan's militarists is ironclad that brooks no denial, and China expresses grave concerns over Japan's erroneous attitude and dishonest practices regarding its history of aggression, Chinese Foreign Ministry spokesperson Lin Jian said on Wednesday. "Comfort women" is a term euphemistically used to refer to women and girls forced into sexual slavery by Japanese militarism in occupied countries and territories during World War II.