Boundary Conditions of analytical nodes refer to the constraints on the nodes. The point where the nodes create intersections of analytical members or intersect with the ground are the boundaries, and the boundary conditions determine the Releases of the nodes, or how the nodes should or should not move. Some nodes must be fixed solid with no movement, some need to be able to rotate freely, and some others should rotate, but only around one axis. You can note this rotation and its percentage using the Releases settings during analytical member placement. When you export your data for analysis, the analytical package notes these conditions and may determine that you need to make changes, depending on the codes you are trying to pass.