Can someone explain the difference between a “block” and a “built-in block” to customize the display of CSS?
Basically, this is a way to make elements inline, but preserving their block capabilities, such as setting width and height, top and bottom margins and scrolling, etc. For example:
(Source: http://www.impressivewebs.com/inline-block/ )
an inline block processes an element like other inline elements, but allows you to use block properties.
Elements with display: the block is as wide as allowed, and usually starts on a new line.
This is a wonderful detailed article on this topic: What is a deal with a display: an integrated unit?