Q about Density found in Mammogram means

I am 47 with no known health issues related to my breasts. I have been getting mammograms for about 10 years post breast reduction because scar tissue makes it impossible to detect anything. I had my annual routine sceening mammogram last Wed. I was called today and told I need to return to recheck certain density changes as well as a possible growth or tumor not seen in the previous mammogram. What exactly does density mean? If it is not considered jjust a normal issue due to aging or breast scar tissue; what can be the causes for this minding?

[Cleveland Clinic]

Dear knightshotter, Breast density refers to the thickness of breast tissue.  In younger women the ratio of dense breast tissue to fat tissue is higher and as we age the density of normal breast tissue lessens as the amount of fat tissue increases.  If there is an area of the breast tissue that is more dense than another that shows up on a screening mammogram further investigation, such as a spot compression and/or ultrasound are needed to further characterize the area. This could be as simple as some tissue folding over on itself in the first mammogram and this will resolve with spot compression. It is not uncommon to be called back for further evaluation. It does not necessarily mean cancer. It just means that further evaluation is needed.