Assigning content to regions
If none are defined, the following values are assumed in Drupal 6.
regions[left] = Left sidebar
regions[right] = Right sidebar
regions[content] = Content
regions[header] = Header
regions[footer] = Footer
Drupal 7 adds Highlighted and Help as default regions. By default, the textual content of the Help region is the same as the $help variable was in page.tpl.php for Drupal 6. The "machine" readable names of the sidebars have also changed names.
regions[sidebar_first] = Left sidebar
regions[sidebar_second] = Right sidebar
regions[content] = Content
regions[header] = Header
regions[footer] = Footer
regions[highlighted] = Highlighted
regions[help] = HelpDrupal 7 bartik theme has following default regions -
regions[header] = Header
regions[help] = Help
regions[page_top] = Page top
regions[page_bottom] = Page bottom
regions[highlighted] = Highlighted
regions[featured] = Featured
regions[content] = Content
regions[sidebar_first] = Sidebar first
regions[sidebar_second] = Sidebar second
regions[triptych_first] = Triptych first
regions[triptych_middle] = Triptych middle
regions[triptych_last] = Triptych last
regions[footer_firstcolumn] = Footer first column
regions[footer_secondcolumn] = Footer second column
regions[footer_thirdcolumn] = Footer third column