Definition of clusters:
(n) :
A bunch or group of several discrete items that are close to each other.
(n) :
A number of individuals (animals or people) collected in one place or grouped together; a crowd, a mob, a swarm.
(n) :
(computing) A group of computers that work together.
(n) :
(astronomy) A group of galaxies, nebulae, or stars that appear to the naked eye to be near each other.
(n) :
(epidemiology) A group of cases of the same disease occurring around the same place or time.
(n) :
(physical chemistry) An ensemble of bound atoms (especially of a metal) or molecules, intermediate in size between a molecule and a bulk solid.