What does the term 'cascade' mean in CSS?

The CSS cascade determines which conflicting style should be applied to an element. It is based on three main criteria:

1. Importance: Styles with !important have the highest priority.
2. Specificity: More specific selectors override less specific ones. Specificity is calculated based on the number of ID selectors, class/pseudo-class/attribute selectors, and element/pseudo-element selectors in the selector.
3. Source order: When importance and specificity are equal, the rule declared last is applied.

Besides these three, other factors are also considered:

• Source of style: User styles (browser settings), author styles (external and internal styles, inline styles), default browser styles.
• Inheritance: Some properties are inherited from parent elements to children.

Example of specificity:

/* Specificity: 0-1-0 */
.my-class {
  color: blue;
}

/* Specificity: 1-0-0 */
#my-id {
  color: red;
}

In this case, the element with id my-id and class my-class will have red text because the ID #my-id has higher specificity than .my-class.