Endoplasm generally refers to the inner (often granulated), dense part of a cell's cytoplasm. This is opposed to the ectoplasm which is the outer (non-granulated) layer of the cytoplasm, which is typically watery and immediately adjacent to the plasma membrane. The nucleus is separated from the endoplasm by the nuclear envelope. The different makeups/viscosities of the endoplasm and ectoplasm contribute to the amoeba's locomotion through the formation of a pseudopod. However, other types of cells have cytoplasm divided into endo- and ectoplasm. The endoplasm, along with its granules, contains water, nucleic acids, amino acids, carbohydrates, inorganic ions, lipids, enzymes, and other molecular compounds. It is the site of most cellular processes as it houses the organelles that make up the endomembrane system, as well as those that stand alone. The endoplasm is necessary for most metabolic activities, including cell division.

The endoplasm, like the cytoplasm, is far from static. It is in a constant state of flux through intracellular transport, as vesicles are shuttled between organelles and to/from the plasma membrane. Materials are regularly both degraded and synthesized within the endoplasm based on the needs of the cell and/or organism. Some components of the cytoskeleton run throughout the endoplasm though most are concentrated in the ectoplasm - towards the cells edges, closer to the plasma membrane. The endoplasm's granules are suspended in cytosol.