Before exploring some of what CSS3 has to offer, to prevent confusion, let's establish the terminology we use to describe a CSS rule. Consider the following example:

.round {
  border-radius: 10px;
}

This rule is made up of the selector (.round) and then the declaration (border-radius: 10px;). However, the declaration is further defined by the property (border-radius:) and the value (10px;). Happy, we're on the same page? Great, let's press on.