Answer:
scale factor
Explanation:
A vocabulary term is what it is. Often, there is no explanation.
To change (multiply by a constant) every dimension of a figure is to scale it; the number by which it is scaled is a scale factor.
Area and Volume are parameters of a figure. Enlargement is the process or the result of the process of making things larger (generally). The enlargment may actually be a reduction if the scale factor is less than 1.
A coefficient is the multiplier of some variable or variable term. It is often a constant, but may not be. An equation involving figure dimensions may use a scale factor as a coefficient, but in general, the terms are unrelated.