Property-Name:
In CSS, "font-size" is known as a property-name. Property-names are used to specify the various styling properties of elements on a webpage. "font-size" specifically controls the size of the text within an element.

Selector, Rule, Property:
- Selector: A selector is used to target specific elements on a webpage that you want to style. It can be an HTML tag, class, or ID.
- Rule: A rule consists of a selector and one or more declarations. Declarations are made up of a property-name and a value.
- Property: Properties are the specific styling attributes that you want to apply to the selected elements. They include properties like "font-size", "color", "background", etc.

Using "font-size" as a Property-Name:
When using "font-size" as a property-name in CSS, you can specify the size of the text within an element. This can be done using different units such as pixels, ems, or percentages. For example:
css
p {
font-size: 16px;
}
This code sets the font size of all `` elements to 16 pixels. By adjusting the value assigned to "font-size", you can control the appearance of text on your webpage.

Conclusion:
Understanding the role of "font-size" as a property-name in CSS is essential for effectively styling text on a webpage. By using property-names correctly within CSS rules, you can create visually appealing and user-friendly designs.