Ultrafiltration refers to the filtration which occurs under high pressure.
In this process, the blood passes through the glomerulus under high pressure. This facilitates filtration of the blood plasma through the thin, porous epithelium of the glomerulus and Bowman capsule’s wall.
Glomerular filtrate or ultrafiltrate contains water, urea, glucose, salts, and other plasma solutes.
Large molecules such as blood cells and large proteins are not filtered by the glomerulus since they don't pass through the epithelium.