Mass in this context is synonymous with weight. So, you can specify the composition of some material in terms of the weight of its components. Let us say, you have a gram of iron, two grams of copper, and four drams of silicon dioxide. that specifies a definite composition by mass.
heterogeneous mixture
A mass.
Matter ( in any form) with a definite chemical composition . Also a umbrella term for drugs( substance abuse)
xanthomaxanthoma
anything which has mass and occupies space
A xanthoma is a yellow nodule or mass. The plural is xanthomata.
A bolus
A mass of tissue growing uncontrollably is a cancerous tumor.
Osteopenia is an abnormal reduction in bone mass.
Luteal means related to a mass of yellow glandular tissue.
A mass of diseased cells is a tumor.
Mass murder, before the term 'Holocaust' was used, Auschwitz was commonly used as a term for the same meaning.