There are a lot of questions here related to Bootstrap. I see a lot of people using it. So I tried to research it, and I found the official Bootstrap site, but there was only a download section and a few words after that. Nothing that explains what is it for... I just understood that it is a front-end helper. I have tried to find something by Googling, but found nothing specific. Everything I found is related to the computer science definition.
So, my questions are:
It is an HTML, CSS, and JavaScript open-source framework (initially created by Twitter) that you can use as a basis for creating web sites or web applications.
Update
The official bootstrap website is updated and includes a clear definition.
"Bootstrap is the most popular HTML, CSS, and JS framework for developing responsive, mobile first projects on the web."
"Designed and built with all the love in the world by @mdo and @fat."