The phrase "hold up his writing is this fire" originated as a reaction meme from a YouTube video thumbnail of a content creator reacting to the songwriting of Billy Joel, particularly in the song "Piano Man." The expression is used humorously on social media to emphasize surprise or admiration for unexpectedly good, impressive, or "fire" writing, such as lyrics, tweets, memes, or other text content from a source. It conveys a sudden realization that the quality of writing is very high or strikingly good.

In this context, "hold up" means "wait a moment" or "pause," and "his writing is this fire" means the writing is exceptionally good, using "fire" as slang for excellent or impressive quality. The phrase as a whole is an enthusiastic callout to the remarkable skill or impact of someone's writing. Thus, the phrase is a popular internet reaction to praise or highlight excellent writing.