cluster
noun [ C ] uk/ˈklʌs.tər/ us/ˈklʌs.tɚ/
[ + sing/pl verb ]（同类物聚集的）串，丛，束，群
a group of similar things that are close together, sometimes surrounding something
Have a look at the cluster of galaxies in this photograph. 看看这张照片上的星系群。
There was a cluster of fans around him, asking for autographs. 一大群崇拜者围着他，找他签名。
phonetics specialized辅音丛（连在一起的两个或以上的辅音）
a group of two or more consonant sounds that are together and have no vowel sound between them
The /str/ at the beginning of "stray" is a cluster. “stray”这个单词的前三个字母str组成了一个辅音丛。