When you are doing online dating ISO stands for in search of. There are many different things a person could be in search of, such as a man, a woman, a transgender person or a cross dresser. You could be in search of someone who is single, divorced or perhaps someone who is looking for something extra in their lives. ISO is usually a precursor to a list of qualities that someone is searching for in their significant other, a date or a hook up. If you see ISO then that means that you should pay attention to what comes next so you’ll know if you’re a good match or not.