Difference between Manages Terms and Enterprise Keywords

Terms can be divided into two types:

• Managed terms, which are usually predefined, can be created only by users with the appropriate permissions, and are often organized into a hierarchy.
• Enterprise keywords, which are simply words or phrases that have been added to SharePoint Server 2010 items. All enterprise keywords are part of a single, non-hierarchical term set called the keyword set.
  
  Difference between Managed Terms and Enterprise Keyword