Block Vs Inline level Elements
HTML Elements are classified as Block Level and Inline Level elements on the basics of their display behaviour. <p> <div> <h1> < h2> <address> etc are block level elements, whereas <b>, <strong>, <i>, <span>, <u> and <s> are inline level elements.
A block level element can have both inline and block elements as children or descendent, but inline elements can have only inline elements as children. (Except anchor tag).