Introduce the topic, including the background information and your research's contribution to the field.
A one-paragraph summary, stating the research question and/or problems and contribution to current knowledge, and succinctly stating methods, results, and conclusions.
Abstracts may be labeled as the introduction
Keep in mind that a research poster is thought of as an illustrated abstract.
See an example at F1000Research (hover over an image for the zoom option or select "View Full Screen" above the image).