Absolute cost advantages.
Stigler.
“A barrier to entry may be defined as a cost of producing (at some or every rate of output) which must be borne by a firm which seeks to enter an industry but is not borne by firms already in the industry.” (The Organization of Industry. Homewood, Ill.: R. D. Irwin, 1968, p. 67.)
George J. Stigler, 1911-1991.