If your research will make a real difference of some sort in the world, and this is fundamentally what is meant by saying your research has an impact. The UK Research and Innovation define two types of research impact:
The demonstrable contribution that excellent research makes to academic advances, across and within disciplines, including significant advances in understanding, methods, theory and application.
Economic and Societal Impact
The demonstrable contribution that excellent research makes to society and the economy. Economic and societal impacts embrace all the extremely diverse ways in which research-related knowledge and skills benefit individuals, organizations and nations.
Research impact can be measured quantitatively by various types research metrics. It can be further defined by:
Research impact can also be demonstrated qualitatively in terms of social and cultural applications and measures of esteem: ARC Research Impact Principles and Framework.