Before revision:  In HRIthis is known as explainability, expressivity, transparencyor sometimes legibility, and the challenge for embodied agents is that they offer a unique array of modalities to communicate this information thanks to their embodiment. Responding to this surge of interest, we review the existing literature in explainability URLanize it by (1) providing an overview of existing definitions,  (2) showing how explainability is implemented and how it exploits different modalities, and  (3) showing how the impact of explainability is measured.
After revision:  In HRIthis is known as explainability, expressivity, transparencyor sometimes legibility, and the challenge for embodied agents is that they offer a unique array of modalities that embodied agents have access to when compared with non-embodied agents. Another reason is that, different authors use these terms in different ways. We, hence, review the existing literature in explainability URLanize it by (1) providing an overview of existing definitions, (2) showing how explainability is implemented and how it exploits different modalities, and (3) showing how the impact of explainability is measured.