What does the term "cascade" mean in CSS?

The cascade in CSS is a system by which the browser determines which styles to apply to an element when different rules are set for it. It takes three things into account, in strict order:

1. Origin (user agent, author styles, !important, inline, etc.)
2. Selector specificity
3. Order of declaration (later wins, if everything else is equal)

The point: the cascade is a conflict-resolution mechanism that picks the final property value for an element when there are competing styles.