Value drift refers to the change or "drift" that our values may undergo over time; 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.)
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).
Aird, Michael (2020) Collection of work on value drift that isn't on the EA Forum, Effective Altruism Forum, April 10.