【Bulk】 , 【mass】 , 【volume】 mean a body of usually material substance that constitutes a thing or unit.

【Bulk】 is applied mainly to what is or appears to be inordinately large or heavy and often more or less shapeless or unshapely.

【Mass】 is applied mainly to something, whether material or immaterial, that is or gives the appearance of being built up by the piling or gathering together of things of the same kind so that they cohere and have a real or apparent unity.

【Volume】 usually applies to something that flows and is therefore without outline and often continuous in extent.

These three terms also come into comparison when they designate quantity or amount. But 【bulk】 and 【mass】 mean the greater part or a large majority of something objective.

【Volume】 , however, may denote either the total amount or quantity especially of something subject to seasonal, periodic, or other fluctuations or a considerable or relatively great amount.