ad hoc comes from Latin and it means "for this", "created for a cetain purpose". When someone comes up with a reason not to do something or to support an opinion.
He hadn`t thought about the matter before, so when we talked he gave me an ad hoc reply.
The systematic study of ad hoc constructions—temporary solutions, situational explanations, one-off fixes—and their role in human affairs. Ad hoc sciences examine how ad hoc reasoning works, when it's appropriate, and how it can be improved. They study the psychology of ad hoc (why we invent what we invent), the sociology of ad hoc (how temporary fixes spread or die), and the history of ad hoc (which temporary solutions became permanent). Ad hoc sciences are themselves somewhat ad hoc—developed for this purpose, in this context, without claiming universality. They're the science of making do, and they make do themselves.
Example: "He studied ad hoc sciences, learning how to generate temporary solutions that worked well enough for now. His dissertation was titled 'The Epistemology of the Temporary: How We Know What Works for Now.' The committee found it either brilliant or ad hoc—they couldn't decide which. He graduated anyway, which was ad hoc enough."
The practice of designing and building solutions for specific, often temporary situations—engineering without the luxury of planning, testing, or mass production. Ad hoc engineering is what happens in emergencies, in remote locations, in startup offices, in any situation where you need something to work now and can't wait for proper engineering. It's the art of the temporary fix, the makeshift solution, the structure that only needs to stand for a while. Ad hoc engineering is despised by professional engineers (who value reliability) and beloved by everyone else (who value results). It's engineering for the real world, where most problems are unique and most solutions are temporary.
Example: "She practiced ad hoc engineering in her apartment, building a bookshelf from cinder blocks and planks, a desk from a door and sawhorses, a headboard from an old fence. Nothing would survive a move; everything worked perfectly here. Ad hoc engineering wasn't permanent, but it was home."