* Large: Red giants are significantly larger than our Sun, often with radii 10-100 times greater.

* Cool: They have surface temperatures ranging from about 3,500 to 5,000 Kelvin, making them appear reddish in color.

Here's how it fits into the classification system:

* Spectral Class: Red giants fall into the spectral classes K and M on the Hertzsprung-Russell diagram. These classes correspond to cooler stars.

* Luminosity Class: Red giants are classified as giants (III) or supergiants (I), indicating their larger size and luminosity compared to main sequence stars.

Examples of red giants:

* Betelgeuse in the constellation Orion

* Arcturus in the constellation Boötes

* Antares in the constellation Scorpius

It's important to note:

* While the term "red giant" is widely used, it's not a formal classification. It's more of a descriptive term for a star that has evolved off the main sequence and is now in a giant phase.

* There are also "blue giants" and "yellow giants", which are hotter and more luminous than red giants.