An endometrial biopsy is a procedure to collect a small sample of tissue from the lining of the uterus for analysis. It is used to investigate abnormal uterine bleeding, diagnose conditions like endometrial hyperplasia or cancer, and assess infertility issues. The procedure involves inserting a small tube through the cervix to obtain the tissue sample, which is then examined under a microscope. It is typically performed in a doctor's office and may cause mild cramping or spotting afterward.