Red shift and blue shift refer to the change in the frequency of light when an object shifts away (red) from and towards (blue) the center of potential energy. Red shift and blue shifts show up in light spectra patterns from objects.
There are to kinds of shifts, gravitational and electric due to the gravitational ( -GmM/r) and electrical potential energy (-e^2/4pi r). The shift is measured by the cos(x) of the angle between the radius of the potential center and the velocity of the object with respect to the center. If the angle is 90 degrees there is no shift or the shift is zero, cos90=0.
If the angle is less than 90 degrees the shift is red and the object is moving away from the center. If the angle is greater than 90 degrees the shift is blue and the object is moving towards the center. At 0 degrees the object is radially moving away from the center and at 180 degrees the object is radially moving towards the center. At 90 degrees the object is moving transverse to the center.
The redshift is the ratio of the 'speed v' of the object to the 'speed c' of light and is designated by z=v/c = cos(x). The gravitational redshift is z=v/c=sqrt(GM/rc^2). The electrical redshift is z=v/c=e^2z/2nh = 2.3e-3/n = alpha/n = Fine Structure Constant.
The redshift indicates that the direction of the object velocity is away from the center, it indicates the object is in equilibrium between the centripetal force and the centrifugal force. The redshift is mis-understood by scientists thinking it indicates an expanding Universe.