Final answer:
The line composed of the data from most stars in the HR diagram is called the Main Sequence.
Step-by-step explanation:
The name for the line in the HR diagram that is composed of the data from most stars we see is the Main Sequence.
The HR diagram is a plot of stellar luminosity against surface temperature. Most stars lie on the main sequence, which extends diagonally across the HR diagram from high temperature and high luminosity to low temperature and low luminosity. About 90% of the stars lie on the main sequence, making it the line composed of the data from most stars.
For example, in the HR diagram, stars that are hotter and brighter are located towards the top left, while stars that are cooler and dimmer are located towards the bottom right. The main sequence line represents stars that are in a stable state, fusing hydrogen into helium in their cores.