The ocean is a huge body of water that is constantly in motion. General patterns of ocean flow are called currents. Sometimes theses currents can pinch off sections and create circular currents of water called an eddy.
You may have seen an eddy if you've ever gone canoeing and you see a small whirlpool of water while you paddle through the water. The swirling motion of eddies in the ocean cause nutrients that are normally found in colder, deeper waters to come to the surface.
Significant eddies are assigned names similar to hurricanes. In the U.S., an oceanographic company called Horizon Marine assigns names to each eddy as they occur. The names follow chronologically along with the alphabet and are decided upon by staff at Horizon Marine. The staff try to think of creative ways to assign names.
For example, an eddy that formed in the Gulf of Mexico in June 2010 is named Eddy Franklin after Ben Franklin, as he was known to have done research on the Gulf Stream.
For more information:
Ocean Mesoscale Eddies, NOAA's Geophysical Fluid Dynamics Laboratory
Center for Operational Oceanographic Products and Services
National Current Observation Program
Currents Tutorial, NOS Education
Diving Deeper Podcast, Episode 15 (August 12, 2009) - What are currents?
Original article: What is an eddy?