decadent, or more over decadence would be something like the following:
You have a culture which developes quiet nicely to its peak but due to oversaturation starts to decay.
The process of decaying simply is that people, who held values and greater visions in high esteem, drop their attitudes and start to satisfy their necessities.
The problem is that the necessities are already more than satisfied due to pure abundance which leads to a creation of even more absurd/stupid necessities which are then satisfied.
The result of this is decreasing vigor and, sooner or later, boredom.
An example would be the late roman empire or our modern culture.
Hope this is understandable (I'm sure, someone could explain this better).