An instant hit is a term used to describe something that becomes popular or successful immediately after its release, introduction or debut. It refers to an event, product, song, movie, book, etc., that gains widespread acceptance and appreciation almost instantly upon being introduced to the public. In other words, it's something that captures people's attention and appeals to a large audience right from the start. The phrase is often used in reference to music or entertainment, where an album, single, movie or TV show becomes popular overnight, attracting a huge following within days of its release.