The phrase comes from the need to separate two near-identical words: astroid, a mathematical curve with four cusps, and asteroid, a rocky body in space. Because the spelling differs by only one letter, the warning is often placed at the start of explanations of the curve to stop readers taking the wrong meaning. Online, creators have lifted that short clarification into a standalone clip, using it as a quick, knowing aside whenever a similar mix-up appears in science, maths or wordplay content.