A coherent region of fluid embedded in a fluid with different properties (air in water) or a coherent region of fluid surrounded by a membrane embedded in a fluid which may or may not be different (such as air in a soap membrane).
A coherent region of fluid embedded in a fluid with different properties (air in water) or a coherent region of fluid surrounded by a membrane embedded in a fluid which may or may not be different (such as air in a soap membrane).