default-tab-width

default-tab-width is a variable defined in `C source code'.
Its value is

8

• This variable is obsolete since 23.2;
  use `tab-width' instead.

Documentation:
Default value of `tab-width' for buffers that do not override it.
NOTE: This controls the display width of a TAB character, and not
the size of an indentation step.
This is the same as (default-value 'tab-width).