Gibson-assembled (and its noun form Gibson assembly) is a phrase coined by Eric Mukherjee to describe questions written by haphazardly joining together clues from lists on Wikipedia, analogously to the molecular cloning method of Gibson assembly. It is now used more broadly to describe tossups which have been created by joining together clues from previous questions without significant alteration.
As part of the Would You Recommend Working for NHBB? thread, Eric Mukherjee criticized the low quality of questions written by Andrew Leung by calling them "Gibson-assembled from lists of named things on Wikipedia".
Gibson assembly is a molecular cloning technique which joins fragments of DNA together into a single strand. Crucially to this analogy, the pieces are joined together without modification and in a single step (i.e. with little effort from the assembler).
Gibson assembly is the lowest-effort method of creating questions and is frowned upon as a result. At best, a Gibson-assembled question is serviceable but unornamented; at its worst, it may involve literal plagiarism of informational sources and past questions. It is generally accepted that questions at lower difficulties involve less "art" and are mechanically simpler to write, especially for sets with length constraints like those of NAQT; thus, there is little utility to referring to them as "Gibson-assembled". The term is thus almost exclusively reserved as a criticism of higher difficulty questions, for which there are expectations of quality and novelty.
While questions at or below normal high school difficulty probably should contain very few clues that have not come up in quizbowl before if they are to meet difficulty guidelines, it is still a bad idea to write questions based on prior questions, for reasons beyond the ethics of plagiarism. Slight misunderstandings and incorrect assessments of clue importance will multiply over time if reliable non-quizbowl sources are not consulted anew for each question. In extreme cases, this can result in the reification of simply wrong clues ("Cavalleria rusticana" is a novel, Vidar's indestructible footwear is called the "Thickmost Shoe," the 1924 Democratic National Convention was called the "Klanbake") based on repetition of clues that someone made up for a packet long ago or that were invented as Wikipedia vandalism and appear in no other source.
Writing tossups via Gibson assembly is a common mistake for newer writers, who may pull clues from question from the archive to the exclusion of all other sources. Such questions are functional but involve little to no new creative input and their close resemblance to past questions makes it easy for experienced writers and editors to notice them (and remove them from their sets if desired).