Never understood this

OCD episode sounds like it could be a short or long period of time where you are ruminating, experiencing intrusive thoughts, etc. Spike sounds like a sudden large increase. Maybe this could be someone who deals with a base-level of OCD and then notices sudden heightened intrusive thoughts. Setback sounds like someone who is on the path of managing their OCD, developing better strategies to avoid rumination, and then they experience a period of time where they feel they have reverted back to their former thought patterns they were fighting to manage. Relapse sounds similar to setback. Setback is a bit more optimistic because it describes a brief moment of weakening during a journey onwards, whilst relapse does not necessarily describe itself as part of a journey but more of a pattern. That being said, setback and relapse are synonyms of each other. I just think setback is used in the context of a journey more.

I’ve best understood this as stressors in life. As stress goes up so does OCD response. A stressful event (like an exam or planning for a wedding) would cause a spike in OCD and if a long duration maybe an episode. Maybe it’s been a while with lower OCD tendencies and then a strong stressful event happens in your life. That would cause you to relapse into strong OCD or set you back. Think about stressful events and situations that cause OCD to fluctuate like a roller coaster.