The acronym POJO stands for Plain Old Java Object—in other words, an ordinary JavaBean. POJOs are (among other things) commonly used to transfer data between the various components and architectural layers of a system, for example between the presentation tier and the web tier of a J2EE application, or more fundamentally, between a service and its client. Complex business objects are often represented as a graph of POJOs; for example, an Invoice POJO might contain a Customer POJO, a list of LineItem POJOs, and so forth.