Tieable halter top?

I’ve had this shirt for a very long time , as you can see from the title I’m not quite sure if that’s the proper name for what this shirt would be called. You take the straps and tie in around the back of your neck. This is in good condition but by the photo there’s that white stain inside the chest area. I’m not quite sure what that is but it’s not noticeable if you have it on. SIZE: L