What is IOU loss?
IOU is a method to address the disadvantage of L2 Regularization which tends to minimize the error of small objects and maximize the error of big objects. The IoU loss considers the bounding box as a unit instead of optimizing the four coordinates independently. Additionally, it normalizes the IoU to $[0, 1]$ regardless of size.
Formula for IOU
$IOU = \frac{Area\ of\ Overlap}{Area\ of\ Union}$
where