This is a general term to describe scarring of the kidneys' tiny blood vessels, the glomeruli, which are the functional units in the kidney that filter urine from the blood. This disease may result in proteinuria (abnormal amounts of protein in urine). A kidney biopsy (removal of tiny part of kidney with a needle) may be necessary to determine whether a patient has glomerulosclerosis, or another kidney problem. Scarred glomeruli cannot be repaired, and many patients with glomerulosclerosis get worse over time until their kidneys fail. This condition is called end-stage renal disease (ESRD), and patients must undergo dialysis treatment or a kidney transplant. 

Links

https://www.mayoclinic.org/diseases-conditions/fsgs/care-at-mayo-clinic/mac-20354696
https://my.clevelandclinic.org/health/articles/5993-glomerular-diseases
https://www.hopkinsmedicine.org/healthlibrary/conditions/kidney_and_urinary_system_disorders/glomerulosclerosis_85,P01475