An exponential function is a function whose variable is in the exponent. The general form is .

An exponential growth function is a specific type of exponential function that has the form y=ab^x, where h=k=0, a>0, and b>1.

An exponential decay function is a specific type of exponential function that has the form y=ab^x, where h=k=0, a>0 and 0<b<1.

In your case the function is y = -1(3^x) and this is not an exponential growth function nor exponential decay function.