Bootstrap is a frontend framework and open source tool for developing websites and applications using HTML and CSS.
Twitter Blueprint was the initial name given to Bootstrap. Mark Otto and Jacob Thornton developed Bootstrap and used Twitter as the framework for consistency. According to Twitter developer Mark Otto:
"A super small group of developers and I got together to design and build a new internal tool and saw an opportunity to do something more. Through that process, we saw ourselves build something much more substantial than another internal tool. Months later, we ended up with an early version of Bootstrap as a way to document and share common design patterns and assets within the company."
The first official release of Bootstrap was August 19, 2011. There are currently three versions of Bootstrap. However, Bootstrap 4 has been announced but its final version is yet to be released.