A hashtag is a word or phrase preceded by a "#" symbol on social media. It is used to categorize and label posts, making it easier for people to find related content. Full definition
Next I took a coat of tan and painted it over the mint using hashtag strokes and doing a much lighter, wide - spread coat. (findingyourjoyinthejourney.com)
It could be a social contest where you encourage followers to use a specific hashtag for a chance to win a year of free appetizers, for example. (fooddrink-magazine.com)