What does the cluster mean?

Answer 1

1. A number of similar things that occur together as a '''group

2. Two or more consecutive consonants or vowels in a segment of speech''' b: a group of buildings and especially houses built close together on a sizable tract in order to preserve open spaces larger than the individual yard for common recreation

3. An aggregation of stars or galaxies that appear close together in the sky and are gravitationally associated

4. A larger than expected number of cases of disease (as leukemia) occurring in a particular locality, group of people, or period of time