In this chapter, we examine a turbulent boundary layer that develops over a thin and wide flat plate (Fig. 6.1). The flow field in the far-upstream conditions is \(V_{0}\hat{e}_1\) , where \(V_o\) is a constant. The plate is fixed to the reference frame in context (the ground frame). We employ a frame-fixed Cartesian coordinate system \(Ox_1(\hat{e}_1)x_2(\hat{e}_2)x_3(\hat{e}_3)\) . The origin of the coordinate system is fixed at a location such that the boundary layer is turbulentTturbulent boundary layer at all locations \(x_1>0\) . The width of the plate in \(\pm {\hat{e}}_3\) is very large, such that the influence of the plate edges is negligible in the zone of interest. Like any other turbulent flows, the velocity field \(\underline{V}(\underline{X},t)\) and the pressure field \(p(\underline{X},t)\) are unsteady and three-dimensional (3D, which means all flow variables vary with all three spatial coordinates, \(x_1\) , \(x_2\) and \(x_3\) ).