The acronym GIS most commonly refers to Geographic Information Systems, the interconnected hardware, software, users, data, and procedures that together form a system for geospatial analysis. GIS can be used to study, analyze, and visualize any phenomenon that has a spatial component. If location plays a role in your research, GIS offers a way to include these spatial features in your analysis.
Many historians have discovered GIS as a tool for looking at their research through a different analytical lense. Historical events, migrations, interactions, and developments can be studied from a spatial persepective, focusing on the "where" rather than the "when."
The video below gives one example of the value GIS can lend to historical research, in this case the perspectives gained by mapping aspects of the holocaust. Please contact me to discuss how GIS could be used in your own research.