An emulsion is a mixture of two liquids that are typically immiscible (don't blend) that forms a two phase system. One of the two liquids is dispersed in the mixture, forming the dispersed phase. The other liquid contains the dispersion and is known as the continuous phase. An example of two immiscible liquids would be water and oil. In general an emulsion will be unstable since the dispersed phase will try to decrease it's surface tension by grouping with other dispersed droplets until the liquids separate again. However, a stable emulsion can be formed by the addition of emulsifiers, such as surfactants that distribute themselves around the interface between the two liquids, creating a stable system. Emulsions are generally regarded as a special class of colloids where both the continuous and dispersed mediums are liquid. However, this distinction is not rigid with some people such as Witten specifying the term colloid only for a mixture of solids and liquids.
A. Two immiscible liquids. B. An unstable emulsion with both a dispersed and continuous phase. C. The unstable emulsion slowly separates. D. An emulsion with a surfactant to stabilize the mixed system.
Soft Matter Examples
Emulsions are an important type of "soft matter". As a system, it has many properties of a liquid but depending on the size of the dispersed phase droplets, the properties of the emulsion will be very different than those of either pure liquid.
Examples of emulsions from everyday life include butter and margarine.
 R. Jones, "Soft Condensed Matter," Oxford University Press Inc., New York (2002).
 Wikipedia "Emulsion"
 T. Witten, "Structured Fluids: Polymers, Colloids, Surfactants," Oxford University Press Inc., New York (2004).
Keyword in references:
All-aqueous core-shell droplets produced in a microfluidic device
Amphiphilic Crescent-Moon-Shaped Microparticles Formed by Selective Adsorption of Colloids
Contact angle associated with thin liquid films in emulsions
Double-emulsion drops with ultra-thin shells for capsule templates
High-throughput injection with microfluidics using picoinjectors
One-Step Emulsification of Multiple Concentric Shells with Capillary Microfluidic Devices
Patterned Colloidal Coating Using Adhesive Emulsions
Reversible aggregation of responsive polymer-stabilized colloids and the pH-dependent formation of porous scaffolds
Patterning Hierarchy in Direct and Inverse Opal Crystals
Liquid-infused structured surfaces with exceptional anti-biofouling performance
Electric-field-induced capillary attraction between like-charged particles at liquid interfaces
Evaporation-Driven Assembly of Colloidal Particles
Self-Assembly of Spherical Particles on an Evaporating Sessile Droplet
Superficial Wrinkles in Stretched, Drying Gelatin Films
Mechanics of Interfacial Composite Materials
Gravitational Stability of Suspensions of Attractive Colloidal Particles
Elasticity of Floppy and Stiff Random Networks
Infochemistry: Encoding Information as Optical Pulses Using Droplets in a Microfluidic Device
Shock-driven jamming and periodic fracture of particulate rafts
Colloidal spheres confined by liquid droplets: Geometry, physics, and physical chemistry
Measuring Dynamics and Interactions of Colloidal Particles with Digital Holographic Microscopy
Self-Assembly of Polyhedral Hybrid Colloidal Particles
Surfactant-Assisted Synthesis of Uniform Titania Microspheres and Their Clusters
Self-Organization of Bidisperse Colloids in Water Droplets
Design and Synthesis of Model Transparent Aqueous Colloids with Optimal Scattering Properties
Structural properties of the sliding columnar phase in layered liquid crystalline systems
Jamming at zero temperature and zero applied stress: The epitome of disorder
Measurements of the yield stress in frictionless granular systems
Comparison of low-amplitude oscillatory shear in experimental and computational studies of model foams
Tuning jammed frictionless disk packings from isostatic to hyperstatic
Minimal Energy Packings and Collapse of Sticky Tangent Hard-Sphere Polymers
Force Distributions near Jamming and Glass Transitions
Velocity Profiles in Repulsive Athermal Systems under Shear
Contact percolation transition in athermal particulate systems
Topology of force networks in compressed granular media
Short-range order and near-field effects on optical scattering and structural coloration