Introduction

Bootstrap is the currently most popular open source framework for developing responsive, mobile-first Web
application and websites.

•  It uses HTML5, CSS3, and JavaScript and jQuery. 
•  Bootstrap helps you kick start the development of webapps and websites. 
•  Bootstrap contains HTML and CSS-based design templates for text, forms, buttons, navigation and other components.  

History: 

•  It's developed by Mark Otto and Jacob Thornton at Twitter as a framework to encourage consistency across internal tools. It's also referred as Twitter Bootstrap. 
•  Its first version was released in Aug 2011 and because of the features it provided, in June 2014 Bootstrap was the No.1 project on GitHub.

Advantage of Bootstrap Framework. 

Mobile-first approach: Bootstrap 3 is mobile first in the sense that the code for Bootstrap now starts by targeting smaller screens like mobile devices, tablets, and then “expands” components and grids for larger screens such as laptops and desktops. 

•   Browser support: Bootstrap is supported by all popular browsers used on internet. 
•  Easy to get started: You don’t have to be a hard core programmer, with just the knowledge of HTML and CSS anyone can get started with Bootstrap. 
•  Responsive web design: Bootstrap's responsive CSS adjusts to Desktops, Tablets, and Mobile phones. 
•  Bootstrap provides a clean and uniform solution for building an interface for developers. 

Major Features of Bootstrap: 

•  Built-in Support for layout, grids, fluid grids, and responsive designs. 
•  Pre-built CSS: Contains global CSS classes for typography, tables, grids, forms, buttons, images, and more 
•  Components: Contains lots of reusable components including Icons, Dropdowns, Navbars, Breadcrumbs, 
• Popovers, Alerts, and many more 
•  JavaScript Plugins: Contains lots of custom jQuery plugins. You can include them all or one by one 
•  Customizable Components: We can customize Bootstrap's components with LESS variables and jQuery plugins to create our own version.