A group or collection of several discrete items that are close to each other, such as galaxies, atoms, computers, cases of a disease, words, bombs, chords, consonants, or a statistically significant subset of a population.

A number of individuals (animals or people) collected in one place or grouped together; a crowd, a mob, a swarm.

(slang) Euphemistic form of clusterfuck (“a chaotic situation where everything seems to go wrong”).

Collect animals, people, or objects into clusters, cover with clusters, scatter or strew in clusters, or distribute objects within such that they form clusters.

To cluster means to form a group or gather together.