In CSS, a pseudo-class is a keyword that is used to select and style elements based on their state or position in the document tree.

In CSS, a pseudo-class is a keyword that is used to select and style elements based on their state or position in the document tree.

The term "pseudo-class" comes from the fact that these selectors resemble classes, which are used to apply styles to elements based on their class attributes. However, pseudo-classes are not actually classes in the traditional sense.

The "pseudo" in "pseudo-class" means "false" or "not genuine". Pseudo-classes are considered "false" because they do not actually represent a class of elements in the HTML document. Instead, they represent a specific state or relationship that an element has to its context or user interaction.

For example, the :hover pseudo-class is used to select an element when the user hovers over it with their mouse. This is not a class that is defined in the HTML document, but rather a state that the element can be in. Similarly, the :first-child pseudo-class is used to select the first child element of a parent element, which is not a class that is defined in the HTML document but rather a position within the document tree.

Therefore, pseudo-classes are called "pseudo" because they represent something that is not truly a class, but rather a state or relationship that an element can have within its context.