If you are not aware of Hashtag, then I will say you would not using any social networking sites in a very large extent. Here I am going to explain you about the advantages of hashtag & how you can implement it in your web projects using php & mysql.
Hashtags are essentially a filter, allowing people to see the conversation associated with that word or phrase. Hashtags is alternative to tags.. Twitter is the first site to introduce the hashtag. But now a days sites like facebook, Instagram, Vine & Tumblr are using this feature in all platforms. If you use the hashtag effectively then you will get the contents across different sites together in a single page.
3. Normal links to clickable Links