what are indeterminate calcifications

I was just informed that my mammogram showed that I have microcalcifications but they are indeterminate as they are heterogenous in the small clusters.  They are recommending that I have a biopsy of two of the four groupings to assess their itiology. I don't understand any of this.

Also the report says, Impression: BI-Rads 4.  What does this means? Is it bad?

[Cleveland Clinic]

Dear Pamig, Microcalcifications are actually very fine specks of calcium that light up on a mammogram. Sometimes they can be an indication of cancer or precancer. Based on their pattern on the mammogram it gives the radiologist clues as to their cause. For instance microcalcifications that are more scattered are probably due to benign (non-cancerous) causes (such as normal wear and tear on the tissue), a “cluster” of microcalcifications may increase concern that there may be an underlying tumor.

A BIRADS  4 rating of an ultrasound or mammogram describes a suspicious looking abnormality that is not characteristic but has a reasonable probability of malignancy, and a biopsy should be considered.  In other words, based on the testing done they cannot rule out that something is cancer.  So to be on the safe side a biopsy of the suspicious area is recommended.

[Pamig]

Thank you.