Counterfactual statements are characterized by the conditional keywords “if-then”, as in “if Obama had not raised the national debt to record levels, unemployment would have been much higher.”
The “counter” part of a “counterfactual” statement is that such a statement may be true even through the event described never happened (or “obtained”). The value of such statements is only apparent if one assumes a non-causally deterministic view of the universe where different circumstances (or decisions by causal agents) could have caused events to turn out differently.
Counterfactuals are intergal to the Molinistic view of the relationship between the sovereignty of God and the limited causal agency of man (in other words, limited free will). Specifically, counterfactuals are what give us reason to believe in the existence of logically possible worlds and the notion that while God certainly does predestine all that happens2 there exist truly free, albeit limited, causal agents such as humans and angels.
Verses that point to the existence of counterfactual (statements that can only be valid if there were a logically possible world where the events described would have obtained if circumstances were different) are Jeremiah 38:17-18, 1 Samuel 23:6-10, Matthew 11:23, 1 Corinthians 2:8, John 15:22-24, John 18:36, Luke 4:24-46 and Matthew 26:24
Note that each of the above statements would be rendered incoherent if they were not true in their counter (not obtained) factual (proposition of truth).