Data visualization is a way of exploring complex patterns or large quantities of data that cannot be easily understood through a simple table or text. In a research poster, it can help you tell a story or make an argument about your findings in a way that's easier for your audience, who may only spend a few minutes with your poster, to understand. Depending on what you want to communicate, there are a variety of different tools that can help you show your findings visually.
For a comprehensive guide on creating data visualizations, visit The University of Tennessee Knoxville's Guide to Data Visualization.