Answer:
exponential decay
Explanation:

is an exponential function, where 'a' is the initial value and 'b' is the exponential factor
When the value of 'b' is between 0 and 1 then it is exponential decay
when the value of 'b' is greater than 1 then it is an exponential growth
In the given exponential function , the value of b is 1/2 that is 0.5
The value of 'b' is between 0 and 1 so it is an exponential decay