What is the meaning of the J value in term symbols I understand how to work out the J values of term symbols.

e.g. a d1 configuration gives J values of 5/2 and 3/2. resulting in 2D 3/2

However I dont understand the meaning of it, and why it arises.
For multi-electron atoms where the spin-orbit coupling is weak, it can be presumed that the orbital angular momenta of the individual electrons add to form a resultant orbital angular momentum $\bf{L}$. 

Likewise, the individual spin angular momenta are presumed to couple to produce a resultant spin angular momentum $\bf{S}$ . Then $\bf{L}$ and $\bf{S}$ combine to form the total angular momentum $\bf{J} = \bf{L}+ \bf{S}$.