Commonly called the Pleiades or Seven Sisters, M45 is known as an open star cluster. It contains over a thousand stars that are loosely bound by gravity, but it is visually dominated by a handful of its brightest members.

[snip]

The Pleiades cluster has been observed since ancient times, so it has no known discoverer. However, Galileo Galilei, the Italian scientist best known for discovering the largest moons of Jupiter and championing a heliocentric model of the solar system, was the first to observe the Pleiades through a telescope. M45 is located an estimated distance of 445 light-years from Earth in the constellation Taurus, though this number is not universally agreed upon. It has an apparent magnitude of 1.6 and can be seen with the naked eye. The cluster is best observed during December.

https://science.nasa.gov/mission/hubble/science/explore-the-night-sky/hubble-messier-catalog/messier-45/