Edema is an abnormal accumulation of fluid in the interstitium or body cavities. It can be caused by increased hydrostatic pressure, reduced plasma oncotic pressure, increased vessel permeability, lymphatic obstruction, or changes in tissue water retention. Edema can be generalized, affecting multiple areas, or localized to a specific part of the body. It can also be classified as pitting or non-pitting depending on whether indentation persists after pressure is applied. Common types of edema include peripheral, pulmonary, and cerebral edema, which affect the extremities, lungs, and brain respectively. Treatment focuses on resolving the underlying cause, reducing fluid retention, and managing symptoms.