EAN or Enriched Air Nitrox is a mixture of gases for which content is the same as air but at different ratios. It has higher concentration of oxygen than the 20.8% found in regular air. EAN is used to reduce nitrogen exposition and saturation into the body. It gives longer bottom times at given depths than regular air.
Nitrox is another name for enriched air which is a gas mix different than normal air. Other possible names are EAN or EANx where x is the percentage of oxygen eg: EAN32. It is named this way because just like most of the air we breath it is a mixture of nitrogen and oxygen. Nitrox has a different ratio of the two gases with higher oxygen percentage than regular air.