ATG and Dynamo are interchangeable words for ATG.
Some times Dynamo refers to ATG Container or Nucleus.
Or any API related to ATG we refer it as Dynamo.
For example ATG extension of HttpServletRequest is called DynamoHttpServletRequest, Servlet extension is DynamoServlet etc.
have a look at
it is used as a container for components
it provide the namespace for component
it also loads and initialize the component