Understanding the difference between default and fluid grids

Bootstrap ships with a 12-column grid system that comes in two varieties.…I am on the Bootstrap website at getbootstrap.com, and if you click on the Scaffolding tab here…on the top of the page, and you click on the link on the left side for the grid system,…you'll see the Bootstrap's default grid system.…As shown here, this is the default 940 wide grid.…It's designed to adapt somewhat via adaptive layout to different screen widths.…The numbers indicate how many columns wide each box is.…

In the first row, there is only one column per box, the next row is grouped into a few columns.…If you roll your mouse over each box here in the documentation, there is a tooltip that…will come up to tell you how wide each box is.…That tooltip only works in the documentation, it's not going to work on your live site.…Now you might be wondering, I just told you this is a 12-column grid, but yet when you…look at this example here on the Bootstrap website, you'll see that it's only 9 columns, why is that?…Well, the whole entire getbootstrap.com site is built in Bootstrap itself.…