Originally this was a non-specific term to describe any congenital anomaly affecting the vascular system, including conditions such as absence or duplication of great vessels (truncal anomalies). Over time the term has acquired a more specific meaning in vascular anomalies practice. It is now referred to lesions in which there is an overabundance of specific types of vessels. Vascular malformations are subdivided into fast-flow and slow-flow malformations. Caution is needed when using the term outside this context, and to avoid confusion with the term vascular anomaly.