Value drift is change in the values held by an individual or a community.
Value drift can be desirable; 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.)
There has been some discussion in the effective altruism community about how good or bad various types of value drift are, how we could try to reduce value drift in ourselves or other people, and what implications rates of value drift have for various other efforts (e.g., for movement-building work).