I Am 49 Year Old Postmenopausal Woman Who Underwent Diagnostic

I am 49 year old postmenopausal woman who underwent diagnostic mammogram for palpable right breast lump. Radiologist did not find any abnormalities in right breast, but identified focal nodular asymmetry 6mm in the medial and central left breast with obscured margins. I have been scheduled for bilateral ultrasound. What does focal nodular asymmetry 6mm mean exactly?