Cell culture involves growing cells from animals, plants, insects, and fungi in culture. This is done because it's easier to do experiments on individual cells than on animals. It's also easier to produce large quantities of proteins from cell cultures than from animals.
Some of the newer cell culture techniques allow stem cells to be grown in culture. Stem cells are special cells that can give rise to multiple cell types when given the proper kinds of hormones and growth factors. These cells are being investigated for possible medical treatments.