Yes that means you have a loose bracket. The bracket is the metal part. That part is no longer glued to your teeth. Go to the orthodontist and he will glue it back on. This happens often and is not a big deal but should be fixed at the orthodontist.
If you are talking about dental braces it is not good for the strings to be loose. The dental braces should be intact to align and straighten the teeth accurately. You should visit the doctor for the braces to be tightened.