The total set of relations that unite, at a given period, the discursive practices that give rise to epistemological figures, sciences, and possibly formalized systems; the way in which, in each of these discursive formations, the transition to epistemologization, scientificity, and formalization are situated and operate; the distribution of these thresholds, which may coincide, be subordinated to one another, or be separated by shifts in time; the lateral relations that may exist between epistemological figures or sciences in so far as they belong to neighbouring, but distinct, discursive practices. . . . The ‘episteme’ is the totality of relations that can be discovered, for a given period, between the sciences when one analyses them at the level of discursive regularities.
Foucault, M. The Archaeology of Knowledge. London: Tavistock Publications. 1985 :191