A "Sternenhaufen" is a German term that translates to "star cluster" in English. It refers to a group of stars that are physically close to each other in space, bound together by gravity. There are two main types of star clusters: open clusters, which contain a few dozen to a few thousand stars, and globular clusters, which are densely packed with hundreds of thousands of stars. Star clusters are important for astronomers because they provide insights into the formation and evolution of stars. By studying clusters like the Pleiades or Hercules Globular Cluster, scientists can learn about stellar life cycles and the dynamics of star systems.