"Bread flour" refers to a type of flour that is specially made for baking bread. It is high in gluten, which helps bread dough rise and creates a chewy texture. Full definition
Add in the 1 tsp instant yeast, and 1 cup bread flour. (raegunramblings.com)
I followed the instructions, only I used bread flour instead of AP. (smittenkitchen.com)
If your starter is 100 % regular flour, then go ahead and replace about 50 - 100 g of bread flour with whole wheat flour in this recipe. (theclevercarrot.com)