What the medical term of "nodular Breast" mean by Mammogram? Is it a risk for cancer?

Not a good term. In a mammogram we are looking for a well defined Nodule(Mass) or cluster of calcifications. What this report says is that your breast image was not uniformly dark(normal). Breast images in younger women can be whiter(reported as dense breasts) but that is entirely normal as long as there is no mass detected. For dense breasts, Radiologist will often add a second imaging test like,Ultrasound orMRI.