Origin: Anc Greek
πλάσμα (noun)/plasma(=something formed or molded, an idol) > πλάσσω/plasso(=create, form, mold)
literally apoplast means the continuality of cell protoplasts in a plant body
By E. Munch (1930) in order to define the water path in plant body.
The symplast pathway is the way in which the water moves from cell to cell in the cytoplasm via the plasma membranes and plasmodesmata. There is also the pathway of the apoplast which is the available diffusional space outside the plasma membrane serving to free flow of water, inorganic ions, sugar, plant hormones and proteins. Water in the apoplast pathway moves from cell to cell via spaces in the cellulose cell walls until it reaches the endodermis.
Naoki Sakurai Dynamic Function and Regulation of Apoplast in the Plant Body, J Plant Res (11) 1998.