Possibility. Something that could have been, could be or could still be, including for instance: subjunctives in text; images that reference potential; openings in space that allow movement; the scope of usability of an object; bodily potential; possible connections between one sound and other in a sequence; or tones of voice that express uncertainty.

Reference: Cope, Bill and Mary Kalantzis, 2020, Making Sense: Reference, Agency and Structure in a Grammar of Multimodal Meaning, Cambridge UK: Cambridge University Press, p. 257.