Bread flour is a type of flour that excells in bread baking.
In other words, all-purpose flour can make cookies, bread, gravy, noodles, etc. and do a good job, but not an excellent job. Bread flour will do an excellent job in bread baking and poor to average job for cookies, gravy, noodles, etc. Gluten is the combination of proteins found in flour, which are created during the mixing of dough. There are also other proteins in wheat flour, which do not form gluten. Gluten is the elastic structure responsible for giving structure to bread doughs.