All these words, as here considered, mean a mass of things that come or are brought together. They all imply that the things are neither merged with one another nor united organically in the resultant mass. Accumulation means that the things have come together by a series of additions rather than all at once. It often implies that the things are of the same kind, such as the accumulation of dust on surfaces, or of money in banks, and does not imply any coherence or organization in the mass gathered.

Collection and accumulation are often used interchangeably, but collection frequently implies a high degree of selection and organization in the mass collected: An accumulation of many specimens is needed when one is preparing a scientific collection.

Aggregation always denotes a mass brought together that forms, in some sense, a coherent whole, but one that has a lesser degree of organization than dose a collection : An industrial empire is often an aggregation of unrelated enterprises.

Conglomeration implies that many different and sometimes even incongruous things are brought together from widely scattered sources or regions: The population of New York City is a conglomeration of many different kinds of people from various countries.