A vesicle is a small "bubble" that can separate two liquids. In biology, vesicles are found in cells and play the important role of transporting materials around the cell. The stable separation of liquids is often accomplished through the use of surfactants or some kind of polymer to forma membrane at the interface of the two liquids. Cells themselves are a kind of vesicle, with the cell wall a lipid bilayer. In the past decade, many groups have been able to create artificial vesicles which can act as models for cells.
There are many potential applications for vesicles. They are currently the focus of intense research for drug delivery, cell modelling, and controllable droplet chemistry. The formation of vesicles also signals a phase transition in some cases, such as in surfactants. Understanding their formation and properties will give us insight into the driving forces involved in soft matter.
 Wikipedia "Vesicle"