Correct Answer is: Hit
Custom dimension values that are user or session scoped affect all hits in the current session, including past hits. If you don't want a user or session scoped custom dimension value to affect past hits from the current session, start a new session before applying the value to a hit.
User or session custom dimension values will apply to all hits from current or future sessions even if the hit they are sent with is filtered from a view (profile).
When filtering based on a custom dimension value, hits are filtered based on the scope of that custom dimension value.
Learn about the interaction of filters and custom dimension values during data processing.