The dense, interior layer of a cell's cytoplasm is its endoplasm. Most cellular processes take place in the endoplasm.
Endoplasm comes from Greek roots endon, "within or inside," and plasm, "shape." It's the innermost part of a cell, aside from the nucleus. Endoplasm is often granular, in contrast to the watery ectoplasm which lies between it and the cell wall. If your biology teacher mentions endoplasm, she’s probably talking about those tiny, single-celled organisms called amoebas.