The cytoplasm (also known as cytosol) is the protoplasm of a cell outside the cell nucleus. It is the gel-like material plus the organelles outside the nucleus, and inside the cell membrane.

Many important functions of a cell take place in organelles, which are like bits of machinery for doing jobs. The cytoplasm is highly structured: it is not some kind of soup, even though it is made out of 75–80% water.

The cytosol contains a complex mixture of cytoskeleton filaments, including the endoplasmic reticulum and the Golgi apparatus. It includes dissolved molecules, and water that fills much of the cell. Due to this network of fibres, membranes and the many dissolved macromolecules such as proteins, the cytosol does not act like a simple liquid.