Turn
fold
A turn is one cycle of rolling and folding laminated dough. A single turn, or letter fold, folds the sheet in three like a letter and triples the layer count. A double turn, or book fold, brings both edges to the centre and then folds in half, quadrupling the layers.
The combination of turns sets the final structure. Croissants usually need three single turns; classic puff pastry takes more, up to six. Too many layers become so thin that they merge, and the pastry loses structure rather than gaining it.
Between turns the dough rests in the fridge for at least 30 minutes. The rest releases the gluten tension built up by rolling and returns the butter to the right firmness. Without it the dough contracts and the butter starts to leak.