Inline: Inline displays an element in the same line as the rest. Specifying any height and width properties will be of no use, as it follows the height and width of the line, of which it is a part.
Block: Displays an element as a block element. It starts on a new line and takes up take up as much horizontal space as they can. Block-level elements do not appear in the same line, but breaks the existing line and appear in the next line.
Compared to display: inline, the major difference is that display: inline-block allows to set a width and height on the element.
Also, with display: inline-block, the top and bottom margins/paddings are respected, but with display: inline they are not.
Compared to display: block, the major difference is that display: inline-block does not add a line-break after the element, so the element can sit next to other elements.