What is an AI Hallucination in Plain English?

https://www.rankbookmarkings.win/gemini-2-5-pro-7-0-hallucination-better-than-2-0-flash-a-deep-dive-into-google-gemini-comparison-and-model-accuracy

I’ve spent over a decade building QA programs for enterprise knowledge systems. Back in the day, if a system gave a wrong answer, we called it a "bug." Today, we call it an "AI hallucination