Over time, our moral values may change, or "drift"; we begin to care more about certain values and less about others.
This can be a good thing; over time, we may become wiser and adopt more sensible positions. On the other hand, we may want to avoid drifting away from positions we currently value highly.
(Imagine talking to your future self and learning that you've moved to the opposite end of the political spectrum. Some people might recoil from this idea and wish to stop the change from happening.)
The Value Drift tag covers posts discussing this drift, whether as a neutral phenomenon or as a problem we can work to avoid.