Wall boundary conditions are used to bound fluid and solid regions. In viscous flows, the no-slip boundary condition is enforced at walls by default, but you can specify a tangential velocity component in terms of the translational or rotational motion of the wall boundary, or model a "slip'' wall by specifying shear. (You can also model a slip wall with zero shear using the symmetry boundary type, but using a symmetry boundary will apply symmetry conditions for all equations. See Section 7.14 for details.)
The shear stress and heat transfer between the fluid and wall are computed based on the flow details in the local flow field.
You can find the following information about wall boundary conditions in this section: