A hashtag, symbolised by the ‘pound’ sign or ‘#’ is a way of organising meta-data within an information system. There’s a technical description for you. Another way to look at hashtags is to see them as 'labels' that enable the same type of information to be grouped together. When it comes to Instagram, hashtags are terms you can apply to your image to make them searchable across the platform. By posting hashtags in the comment or caption section of your image, you allow other people to see the image when they search for that term.