Mass and Volume refer to to the metric quantity of a serving size. The Serving Name field refers to the serving size shown on the product's nutrition facts label. A nutrition facts label reports metric quantity using mass or volume. Examples of mass include measurements using ounces and grams. Examples of volume include measurements using fluid ounces and milliliters (e.g. liquid measurements). The serving name, mass, and volume fields are optional; you may create a custom food without entering these details.
For example, a product label might read as follows: Serving Size 1 cup (228g). If you were to create a custom food using these details, mass would be reported as 228. The entry field for volume would be kept blank or entered as 0.