adjective/də dɛ.ʁjɛʁ le fa.ɡo/
very special, that one has been keeping preciously, that one has been keeping up one's sleeve (with the implication that it is excellent, exquisite)
“un petit vin de derrière les fagots” — a really special wine, good stuff
In reference to a bottle of wine that one would keep in a secret location, hidden from sight, and draw out for special occasions.