The region inside a cell including the nucleus is called the cytoplasm.

Here's a breakdown:

* Cytoplasm: This is the gel-like substance that fills the cell and surrounds the nucleus. It's composed mainly of water, salts, and proteins.

* Nucleus: The nucleus is the control center of the cell, containing the cell's DNA and responsible for regulating cellular activities.

So, the cytoplasm is the entire space within the cell membrane, excluding the nucleus.