The term CO-___ can refer to three different words. The first is OPT, which stands for Optional Practical Training. This is a program that allows international students in the United States to gain practical experience in their field of study. The second is ASSN, which stands for Association. This is an organization of people with common interests or goals who come together to work towards a shared purpose. The third is COLDFRONT, which stands for Cold Front. This is a weather phenomenon where cold air moves into an area, bringing cooler temperatures and often precipitation.