This term refers to the exponential function with base $e$ raised to the power of $4x$. The value of this function increases rapidly as $x$ increases.
Exponential function: A mathematical function that increases or decreases exponentially as its input changes.
The inverse operation of exponentiation with base $e$, used to undo exponential growth or decay.
Base: The number being raised to a power in an exponential expression. In this case, the base is $e$.