A podocyte is a special kind of epithelial cell. They are called podocytes because they extend foot processes, but I will go into that in a minute. These cells are located in Bowman's Space, which is a part of the nephron, in the kidney. See that link for more reference, which may be necessary for understanding this node. The podocytes form the third part of the glomerular filtration barrier. These cells extend foot processes about the loops of the glomerular capillaries. They press close together, forming a filtration slit diaphragm. This allows only water and small molecules through. Really, this layer should not see too many unfilterable particles, because it is the last, following the basolateral membrane and the capillary endothelium. If proteins or erythrocytes make it through the barrier, this is a sign of kidney failure.
These are my interpretation of my lecture notes, but I may have used some references from Hole's Anatomy and Physiology (Shier, Butler, Lewis) and Human Physiology (Vander, Sherman, Luciano)