What do we call the fluid outside the organelles but inside the plasma membrane?

The fluid outside the organelles but inside the plasma membrane is specifically referred to as cytosol. Cytosol is the part of the cytoplasm that does not include organelles, which makes it the semi-fluid component in which other cellular structures are suspended. It is primarily composed of water, salts, and organic molecules.

Cytoplasm includes all the contents within the plasma membrane, excluding the nucleus, which encompasses both the cytosol and the organelles. Protoplasm generally refers to the living substance within a cell, which could be interpreted as including both the cytoplasm and the nucleus. The extracellular matrix refers to the network of proteins and molecules outside of cells that provide structural and biochemical support to the surrounding cells; it is not contained within the plasma membrane. Therefore, the designation of cytosol is indeed the most precise term to describe the fluid specifically within the parameters stated in the question.