An emulsion is a solution of one liquid in another liquid.  When two liquids, which normally do not mix with each other are added together, an emulsion is obtained.  An example is a mixture of oil and water.  The size of the droplets can change over the liquid and they are not static. 

If there is more water than oil in the solution, the solution is called water in oil solution.  If there is more oil than water, the solution is called oil in water solution.

The yolk of an egg is also an emulsion. 

Stabilization of an emulsion
An Emulsion is an unstable solution.  In a solution of oil in water, over time, the oil and water will start to separate.  This will eventually result in two separate constituents.    Emulsifiers are substances which will stabilize an emulsion. Emulsifiers work by making the droplets in an emulsion remain separate.  This ensures that one constituent remains suspended in the other constituents.

Emulsions paints are used to paint homes.  They have a rich matte finish. The emulsions consist of small droplets, such as vinyl, which are suspended in water.  They can be applied on walls and ceilings.