They are different ways of describing the same overall thing (describing the whole 'process' of WDW photos.)
Basically: Photopass is the name of the "shooting" of the photos. (Pictures are taken by "Photopass Photographers.") MemoryMaker is the method that "pays for" (and allows you to download) your complete accumulated file of photos.
Photopass with an AP will give you all the photos taken by photopass photographers and attractions for 1 year before the photos expire. You’ll also get bonus photos, but they expire much sooner.
Photopass with an AP will give you all the photos taken by photopass photographers and attractions for 1 year before the photos expire. You’ll also get bonus photos, but they expire much sooner.