What is meant by the following statement? The cell membrane is said to be fluid.

the meaning is that the cell is filled by choroplast.

Individual lipid and protein molecules of the cell membrane are free to move laterally in the plane of the membrane.

Explanation:

Cell membrane is the lipid bilayer made of two layer of phospholipids in which proteins are embedded. The cell membrane is fluid because most of the interactions among proteins and lipids as well as between various phospholipids molecules of the membrane are non-covalent. These interactions allow the individual lipid and protein molecules free to move laterally in the plane of the membrane.