Halliday & Matthiessen (1999: 154, 134):
Medium and Process form the nucleus of the whole figure — that part of the figure which is essential to the complementarity of unfolding and persisting (cf. Figure 4-3 above). The participant functioning as Medium may be affected in various different ways, depending on the particular domain — the 'trace' may b[e] physical, mental, and so on; but the status of Medium generalises across these domains.
