The three terms describe two different things at once, which is why they are so often confused in enquiries. Chopped and leaf describe how the spinach was cut. Portioned describes how it was frozen and presented. A product can be chopped and portioned, chopped and free-flowing, or whole leaf in a block.
Leaf spinach keeps the leaf substantially intact, sometimes with the petiole removed. It is bought where the leaf has to be visible in the finished dish, and it is the most demanding form to handle because intact leaves mat together and are easily broken.
Chopped spinach is cut, typically to a nominal length in the range of 10 to 30 millimetres depending on the specification, and is the standard industrial form. It handles better, doses more accurately by weight, and disperses evenly into a recipe.
Portioned spinach refers to the presentation: after blanching and pressing, the product is formed into discrete portions, commonly nuggets or briquettes of roughly 20 to 60 grams, or into a moulded block. Portions are convenient for retail and for controlled dosing, and they are usually a denser product than free-flowing chopped spinach because pressing removes water.
That water removal is the commercially important variable. A pressed or portioned product carries less water per kilogram, so it is not price-comparable to an unpressed one on a per-kilogram basis. Two spinach quotations that look far apart are frequently the same value once water content is normalised.
So the specification must state, separately: the cut form, the presentation, whether the product is pressed and to what degree, the dry matter or drained weight where either is critical, and the piece or portion weight for a portioned product. Buyers should also state expected yield after cooking, because that is the number the kitchen or the recipe actually depends on.