What does fibroglanduar densities b mean ?

The question should have been clearer to give you the best answer, if you had mentioned you were talking about mammogram. I would assume you are, it is not something that you should worry about it is the radiologic terminology of explaining the relative amount of fibrous tissue compared to glandular tissue in the breast. It does not mean there is cancer.

That medical term is used for breast images by mammogram. Breast composition can be normal or dense (normal or high fibroglandular density in medical term) when mammogram is read.