Here is how Wikipedia defines the #Hashtag:
A hashtag is a word or an unspaced phrase prefixed with the number sign (“#”). It is a form of metadata tag. Words in messages on microblogging and social networking services such as Twitter, Facebook, Google+ or Instagram may be tagged by putting “#” before them, either as they appear in a sentence, (e.g., “New artists announced for #SXSW2014MusicFestival”) or appended to it.
We can say that Hashtags make it possible to create searchable terms or put more emphasis on a word or phrase. My take on hashtags are that they are a great tool to use in marketing and branding, and should be used differently in each social media platform and differently for each business. Not all industries and platforms are the same.
Hashtags on Different Social Media Platforms:
Twitter: Where it all began. Using #hashtags in your Tweets expands your message to new people as the hashtag puts your content in that searchable conversation. Tweet during ‘live’ events using the hashtag, create a hashtag for your own business #JeepLid, or from a Air conditioner company, it’s #Hot outside is your #AC keeping you cool inside?. Another great use of the #Hashtag in twitter is to localize conversations and target the geographical area that is important to your business or brand #InBend. I would recommend using no more than two hashtags in each tweet when relevant.
Instagram: Though Instagram is an image-driven site, hashtagging is common practice and some instances you’ll find it like #Hashtagging on steroids. Because Instagram is image based using multiple hashtags won’t clutter the message because most people or engaged with the image being the message and not the post. I find if you want to overdue hashtags, this would be the platform that is much more forgiving.
Pinterest: Unlike on Instagram, captions aren’t often read on Pinterest. Text on the image is what counts for pin-ability, but adding hashtags and text in your captions is key for search-ability. Pinterest is a platform where redundant and crammed hashtags are okay and will work. Like with any social media platform engagement is most important and you’ll want engagement on your boards, so keep a coherent sentence or two before tacking on some relevant, search-friendly hashtags.
Facebook: Though you can now search hashtags on Facebook, proceed carefully as a large portion of the Facebook audience is still unaware of the use and function of the Hashtag. While you can increase reach by using hashtags; ie. trending topics, hashtags have yet to become fully embraced on Facebook. My advice is to use only one hashtag per post and only use when relevant. I wouldn’t use them in more than 20% of my brand’s posts.
Google+: Google+ unlike Facebook is a hashtag-friendly place. When using #Hashtags on Google + use them when they serve a productive purpose. Nobody’s #wants to #wade through a #sea of #hashtags as #ThisCanJustBeAnnoying.
If you want to learn a little more about #Hashtagging you can watch this skit from SNL with Jimmy Fallon and Justin Timberlake.