If you wanted to be specific, that would be a very long list and depend on the style. We have a lot of names for haircuts in the U.S. If you describe the cut in more detail, I could probably tell you the name of the style. If you were speaking in a more general way, you could say the following: "They wear their hair short/long." "They wear their hair cut short/long." "They have their hair cut to their _____ (whatever the longest point the hair reaches to is e.g. their shoulders, mid-back, waist). "Their hair extends to their _____ (shoulders, mid-back, waist). I hope this answer helps. Let me know if you have more questions.