The physical characteristic that refers to the mass of a substance contained within a specific volume is known as density.

Density is defined as the mass per unit volume of a material and is mathematically represented as:
Density (ρ) = Mass (m) / Volume (V)

- This property helps us understand how compact or concentrated a substance is.
- For example, a substance with a high density means it has a large amount of mass packed into a small volume.
- It is an intrinsic property of materials and plays a crucial role in various fields such as physics, chemistry, engineering, and medicine.

- Viscosity refers to a fluid’s resistance to flow.
- Surface tension is the elastic tendency of a fluid surface that makes it acquire the least surface area possible.
- Elasticity is the ability of a material to return to its original shape after deformation.

Therefore, the correct answer is Density because it specifically describes the relationship between mass and volume of a substance.

Reference: Principles of Physics, Volume 1, Chapter 3, Page 45.