A cluster is a collection of data objects which are similar to one another within the same cluster and dissimilar to the objects in the other clusters. Data mining is the process of semi-automatically analyzing large databases to find useful patterns where the prediction based on past history. Some of the prediction mechanisms include classification, regression, clustering and association. Clustering is the classification of objects into different groups, or more precisely, the partitioning of a data set into subsets (clusters), so that the data in each subset (ideally) share some common trait – often according to some defined distance measure.