The following paragraph is my own opinion and is not a classic definition.

Enterprise application  are the applications which are used in enterprises or has the behavior like them .As you know enterprise  means “A business organization” so a business organizations may need a system with different subsystems serving different departments of the organization. Such an application can be developed with an architecture that best matches functional and non-functional requirements of the project and the point is that there is no fixed architecture for this.
Technically Enterprise Applications are often multi-user systems consisting of two or more interacting subsystems. Generally such applications have transaction concurrency, user load, better subsystem encapsulation, subsystem interaction issues………