Keyword grouping (also called keyword clustering) is putting related search terms into buckets so each bucket becomes one content piece. It stops you writing 5 blog posts or 5 videos that all target the same topic and end up competing with each other.
It finds shared root words across your keyword list (ignoring stop words like 'how', 'to', 'the'), then groups keywords that share the same root. It's fast and free — not as clever as paid clustering tools, but good enough for planning content pillars.
For a single video or blog post, 5 to 15 related keywords is a sweet spot. Larger groups often mean you should split them into a series or content pillar instead of one piece.