Exponential

[Sarah]

Pertaining to exponents; involving variable exponents; as, anexponential expression; exponential calculus; an exponentialfunction. Exponential curve, a curve whose nature is defined by meansof an exponential equation.-- Exponential equation, an equation which contains an exponentialquantity, or in which the unknown quantity enters as an exponent.-- Exponential quantity (Math.), a quantity whose exponent isunknown or variable, as ax.-- Exponential series, a series derived from the development ofexponential equations or quantities.

[Sarah]

Applies to any rate of growth which is larger than some expected rate of growth.

In common usage, however, only a small sample size is available, and exponential applies to sufficiently large positive rate of growth.

In mathematical terms, exponential growth is superlinear

[Sarah]

A very large quantity.

[Tariq Zaki]

A sophisticated [mathematical] term that describes [rapid] [growth] of imaginary things, or things that can’t be measured

[Donald Trump]

(of an increase) becoming more and more rapid.