To "leave a comment" means to provide feedback, opinions or thoughts about something. It usually refers to making an observation or expressing an opinion in response to someone else's work, such as a blog post, article, video, or photograph. The phrase can also refer to leaving a note, message, or remark on social media platforms like Facebook, Twitter, and Instagram. In general, "to leave a comment" means to share one's thoughts in writing about something that has been published or displayed by someone else.