So, I was under the incorrect assumption that the term "gaffe" referred to creating something that just looks close enough to pass on screen. I'm certain I heard this term used for barnum and bailey's "mermaid" creation. Now I want to know what the correct term for this is... I understand that this is technically what you would call special effects. but I'm looking more for the term when it is not a custom made "prop" but a slopped together prop that only looks good when not closely scrutinized.
Props generally fall into two categories; "Hero" (those that can stand close scrutiny, often with working parts and lights) and "Stunt"
A “stunt” version of a prop is typically a low-quality version of a “hero” or detailed prop so that the “hero” version is neither destroyed nor causes harm to the people involved with the stunt. For instance, in the fight scene between Kara Thrace and a Number Six in “Kobol’s Last Gleaming, Part II,” a stunt version of the Arrow of Apollo (made of rubber) was used in that scene. There were two versions of metal and two of rubber made. Stunt versions of props are typically of rubber. Stunt versions of costumes will be the same quality, though specifically marked “stunt”. They may be old versions of the costume, used by the main actor and then given for use by the stunt actor, or they may be new versions, specifically tailored for a stunt actor.