Red Giant: A red giant is a large, cool, and luminous star that has exhausted the hydrogen in its core and is fusing hydrogen in a shell around the core. These stars have a reddish appearance and are much larger than the Sun.
Supergiant: A supergiant is an extremely large and luminous star, often hundreds of times the size of the Sun. Supergiants are the largest and most massive stars in the universe, with very short lifespans.
H-R Diagram: The Hertzsprung-Russell (H-R) diagram is a scatter plot that displays the relationship between the absolute magnitudes and spectral types or surface temperatures of stars. It is a fundamental tool in understanding the properties and evolution of stars, including giants.