micelle (pronounced /maɪˈsɛl/ or /maɪˈsiːl/, plural micellesmicella, or micellae) is an aggregate of surfactant molecules dispersed in a liquid colloid
A typical micelle in aqueous solution forms an aggregate with the hydrophilic "head" regions in contact with surrounding solvent, sequestering the hydrophobic single-tail regions in the micelle centre.
Micelles are approximately spherical in shape. Other phases, including shapes such as ellipsoids, cylinders, and bilayers, are also possible. 
The process of forming micelles is known as micellisation and forms part of the phase behavior of many lipids according to their polymorphism.