Recently I have heard from many Web designers that they use Boilerplate for developing their themes. Can anyone explain what exactly it means? Is it another framework to develop the theme on just like Bootstrap?
Boilerplate is another front-end framework, much like Bootstrap or Foundation but it's a lot more lightweight. It doesn't contain tonnes of cool JS and CSS goodies but provides a solid foundation for building a HTML5 website which will be cross-browser compatible. It basically just speeds up development without bogging you down with tonnes of stuff you probably don't want or need.
I would word it differently, it's another half-assed HTML and CSS framework for pissing out inaccessible bloated poorly written sites while completely defeating the ENTIRE point of writing HTML and using CSS in the first place! Of course that it's also built around the idiotic rubbish known as HTML 5 isn't exactly encouraging.
HTML5 and CSS 3 give a best way to create the most modern and fast performance based website like Bootstrap and Boilerplate framework.
Probably the same as Jonestown -- Grape... though technically it was a generic knockoff and not the actual Kraft brand product.