If you've used Twitter, you've probably seen a hashtag. That is, a hash sign (#) followed by a sequence of characters, e.g. #wine. There's no built-in meaning to hashtags. It's just a textual convention which has become an accepted part of using Twitter. When people use the same hashtag to categorize their tweets, it becomes useful.
For example, Paul Mabray of VinTank has been know to include the hashtag #atomicfireball in his tweets. Who knows what it means? On the other hand, the #redsox hashtag has a pretty obvious meaning, and is used by enough people to break into the "Trending Topics" list you'll see on the right-hand side of your Twitter home page.
If you're curious about ways to use these cryptic constructs to promote your winery more effectively via Twitter, here's a useful and informative article: How to Use Twitter Hashtags for Business
As with all social media forms, Twitter hashtags require an investment of time (and thought) to pay off. The article contains links to some tools and sites which can help.