1. noun A word or phrase (written without spaces) preceded by the pound sign or hash mark (#) in a post on social media, meant as a way to add additional information, humor, or a searchable tag to the post. "Hashtag" is sometimes said humorously in conversation as well. She used the "unedited" hashtag, but that picture looks too good to not have a filter. A: "What a great day we've had!" B: "I know! Hashtag blessed."

2. verb To mark a post with such a hashtag. She hashtagged that picture "unedited," but it looks way too good to not have a filter.