What does impulsivity mean in terms of behavior?

[Daywalker]

This is a good definition:
Impulsivity is broadly defined as "actions without foresight" that are "poorly conceived, prematurely expressed, unduly risky, or inappropriate to the situation, and that often result in undesirable outcomes.

Its not the subject ( shopping,  gambling, sex etc etc )  but the behaviour.
This might help identifying.