gnus-group-line-format

gnus-group-line-format is a variable defined in `gnus-group.el'.
Its value is

"%M%S%p%P%5y:%B%(%g%)
"

Documentation:
*Format of group lines.
It works along the same lines as a normal formatting string,
with some simple extensions.

%M Only marked articles (character, "*" or " ")
%S Whether the group is subscribed (character, "U", "K", "Z" or " ")
%L Level of subscribedness (integer)
%N Number of unread articles (integer)
%I Number of dormant articles (integer)
%i Number of ticked and dormant (integer)
%T Number of ticked articles (integer)
%R Number of read articles (integer)
%U Number of unseen articles (integer)
%t Estimated total number of articles (integer)
%y Number of unread, unticked articles (integer)
%G Group name (string)
%g Qualified group name (string)
%c Short (collapsed) group name. See `gnus-group-uncollapsed-levels'.
%C Group comment (string)
%D Group description (string)
%s Select method (string)
%o Moderated group (char, "m")
%p Process mark (char)
%B Whether a summary buffer for the group is open (char, "*")
%O Moderated group (string, "(m)" or "")
%P Topic indentation (string)
%m Whether there is new(ish) mail in the group (char, "%")
%n Select from where (string)
%z A string that look like `<%s:%n>' if a foreign select method is used
%d The date the group was last entered.
%E Icon as defined by `gnus-group-icon-list'.
%F The disk space used by the articles fetched by both the cache and agent.
%u User defined specifier. The next character in the format string should
be a letter. Gnus will call the function gnus-user-format-function-X,
where X is the letter following %u. The function will be passed a
single dummy parameter as argument. The function should return a
string, which will be inserted into the buffer just like information
from any other group specifier.

Note that this format specification is not always respected. For
reasons of efficiency, when listing killed groups, this specification
is ignored altogether. If the spec is changed considerably, your
output may end up looking strange when listing both alive and killed
groups.

If you use %o or %O, reading the active file will be slower and quite
a bit of extra memory will be used. %D and %F will also worsen
performance. Also note that if you change the format specification to
include any of these specs, you must probably re-start Gnus to see
them go into effect.

General format specifiers can also be used.
See Info node `(gnus)Formatting Variables'.

You can customize this variable.