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Here is a description of the items in the Render Settings window for selecting and creating a Render Pass (the next page Managing Render Passes cover the topics in details):
Current Render Pass
This option menu lists all Render Pass currently in the scene. The selected one is used for all renderings launched using Render Current Frame or Batch Render options of Maya’s Render menu. By default there is only one Render Pass and it is named 'renderPass1'.
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