Vim indentation options

• tabstop: how many columns a tab should be made up of in the editor view.
• expandtab: when enabled, insert the appropriate number of spaces when in insert mode.
• shiftwidth: how many columns text will be indented when using indent operations (such as << or >>) in normal or visual mode
• softtabstop: when enabled,
  • softtabstop < tabstop && noexpandtab, this will result in a combination of tabs and spaces to make up the total spacing .
  • softtabstop == tabstop && noexpandtab, this will always force the use of tabs.
  • expandtab, the value of softtabstop will be ignored and spaces will be forced
• shifround: round indent to nearest multiple of set shiftwidth on indent operations (>> << in Normal mode, CTRL-T CTRL-D in Insert mode)

Source: A byte of Lox (Tabs, stop! The truth about tab and spaces in Vim)