An economic factor that makes it difficult for a business to enter a market and compete with existing suppliers.

"Strictly speaking, a barrier to entry is a condition that makes the long-run costs of a new entrant into a market higher than the long-run costs of the existing firms in the market; a good example is a regulatory limitation on entry. The term is also used, more questionably, as a synonym for heavy start-up costs."
  - Richard A. Posner, Economic Analysis of Law, 10.8, at 227