CSS - Clear Property

About

The wiki/CSS/Properties/clear property indicates which sides of an element's box(es) may not be adjacent to an earlier floating box.

Example

h1, h2, h3, h4, h5, h6 {
    clear: left; /* All header may not be adjacent to a left floating box */
}

Clearfix

A clearfix is generally used in float layouts to constrained the floated element to stay in its container. See float layout