Old objects are traditionally thrown from windows in parts of Italy on New Year's Eve to symbolize letting go of the old year.
The custom reflects a symbolic clearing-out: unwanted possessions from the past year are discarded so that the household can begin anew. Accounts often mention household items such as crockery, furniture, or other objects, but the practice is regional rather than a universal Italian rule.
The tradition is especially associated in popular accounts with southern Italian cities, including Naples. In modern cities, throwing heavy objects from windows can be dangerous and is discouraged or no longer practiced in many places. The historical custom should therefore be understood as a cultural symbol, not advice for a contemporary celebration.
This answer is intentionally broader than “plates” or “furniture.” Different descriptions identify different discarded items, and the objects changed according to local custom and household circumstances. The stable idea is the ritual rejection of old possessions as the new year begins.