New layout mode introduced with CSS3
Allows developers to create flexible layouts without having to rely on floats or inline-block elements
Is direction-agnostic as opposed to the regular layouts (block which is vertically-based and inline which is horizontally-based)
Widely supported across all modern browsers
See the full list of layout modes here
Vertically centering a block of content inside its parent
Making all the children of a container take up an equal amount of the available width/height, regardless of how much width/height is available
Making all columns in a multiple column layout adopt the same height even if they contain a different amount of content