A headband is a band you wear around your head. People put one on to keep hair off the face, to catch sweat in sport, or because it looks nice. Some are soft cloth or elastic and sit across the forehead; some are a hard hoop that slides into the hair. English still calls that hoop a headband, though actually shops in Taiwan often split the two: the soft kind as 髮帶 and the hard kind as 髮箍. It is an ordinary object word, not slang. You will hear it in sport, in fashion, and in kids' dress-up (a frog headband, a cat-ear headband). It is not the thing that goes on your ears and makes sound, and it is not a cloth you wrap around a cut.