What is the cell type "primary cell type" referring to?
A cell that is harvested directly from a living organism.
Primary cells are cultured cells freshly derived from a living organism. Once in culture they undergo a limited, predetermined number of cell divisions. For this reason, primary cells can be passaged a finite number of times and are considered to be very delicate and sensitive.
Cell lines, in contrast to primary cells, typically undergo unlimited cell division and have an infinite lifespan. These are in contrast to immortal cell types.