A clip show is a type of episode that uses large pieces of material from previous episodes within their original context. Their presence is justified as the excerpts being vivid memories of the cast that they recall with one another. The 'now' of the episode thus is (supposed to be) new material. Clip shows entered the webisode series in 2012 during Volume 3 and were brought back in 2015 during Volume 5.
Not every piece of reused animation signifies a clip show. For instance, Spectra's search for a scoop early in "Best Ghoulfriend" reuses a lot of animation from "Ghosts with Dirty Faces", but not the sound. The shots are presented as a new event, separate from what happened in "Ghosts With Dirty Faces", and so it is not part of the "clip"-portion of the clip show.
Clip shows were invented back in the days when reruns were unlikely and internet didn't exist. They used to serve a purpose in reminding the audience of all that had happened in episodes previously and helping a potential new audience to get acquainted with the story. Nowadays, these points are largely moot, and a series of online episodes in particular seems to lack need of clip shows. Nonetheless, Mattel decided on a handful of them for Volume 3 and Volume 5.