1) 每三个月 = every three months He flies to Reykjavik every three months. He was here this March, so next time he is here again will be this June. 2) 每隔三个月 = every other three months He flies to Reykjavik every other three months. He was here this March, so next time he is here again will be this July. Hence, you say in English, i) The Summer Olympic Games are held every four years. ii) The Summer Olympic Games are held every other three years. iii) The Summer Olympic Games are held every fourth year. All are correct.

every third months 是每隔三个月 every three months 是每三个月

每 is short of 每隔