Multimodal interaction is a research field and academic concept focused on how humans communicate and interact using multiple distinct modalities (e.g., speech, gesture, gaze, touch) simultaneously or sequentially. This area investigates the coordination, integration, and interpretation of these diverse modes to understand human communication processes or design more natural, robust, and flexible interactive systems. Its significance lies in leveraging the complementary nature of different modalities to enable richer and more effective communication and interaction.