I'm apologizing for such simple question, I just started to learn string theory. If one end of an open bosonic string is attached to a Dp-brane it means that in directions normal to the brane Dirichlet b.c. are satisfied, and in tangential directions Neumann b.c. are satisfied. Each textbook I checked says that an end point of a string is just pined to the brane, but such descriptions ignores Neumann b.c. in tangential directions. It looks to me that Neumann conditions mean that the string is orthogonal to the D-brane. Is this right?
The endpoint is pinned in the sense that it can only move in the world volume of the brane. A good visual, I think, is a normal string with a small loop at the end that is tied loosely around a fixed rod. The string moves freely in the direction parallel to the rod, but is fixed in the directions perpendicular to it. This would be like a D1 brand.