This is an explanation of the variables compiled by MKStats, and which files these vars are in.

# = 0-9
DATESTRING = 960124 = Jan 24, 1996
MONTHSTRING = 0124 - Jan 24, 1996

sub.readlog.*:

$lineerrors: The of lines in the access_log that did not follow the correct format and could not be counted.
$null: The number of entries in the access_log with (null) as the requesting site (errors).
$totallines: The number of lines of the access_log processed in this run.
$statuscodes{###}: The number of times each status code was returned by the server.
$bytes{DATESTRING}: The number of bytes transferred on the specific day.
$totalbytes: The number of bytes transferred.
$totalhits{DATESTRING}: The number of hits for a specific day, including all images and other files.
$cachehits: The number of times an IP address was pulled from the DNS cache (if resolving is on)
$total: The total number of page hits (not including images and other files)
$dates{DATESTRING}{PAGE}: The number of hits for a specific page on a specific day.
$pagebytes{PAGE}: The number of bytes transferred from a specific page.
$domains{DOMAIN}{MONTHSTRING}: The number of hits from a domain for a specific month.
$domains{DOMAIN}{total}: The total number of hits from a specific domain
$hours{##}: The number of hits for a specific hour of the day.
$users{USER}: The number of hits from a specific user who logged into a secure page or site.

sub.agent:

$agenttotal{BROWSER}: The number of hits from the browser with a specific name.
$agent{BROWSER}{VERSION}: The number of hits from a specific version of a specific browser.

sub.error:

$errors{ERROR}: The number of errors with a specific string.

sub.referer:

$imagecount: The number of images or CGI scripts referenced from off-site.
$images{TO}{FROM}: The number of times the image or CGI in "TO" has been referenced from the site "FROM".
$totalreferer{TO}: The number of times a page has been referenced from an off-site link.
$news: The number of references coming from usenet news articles.
$newsrefs{TO}: The number of usenet news references to a specific page.
$bookmarked: The number of references coming from a bookmark or local file.
$bookmarks{TO}: The number of bookmark references to a specific page.
$searches{yahoo|lycos|webcrawler|infoseek|altavista}: The number of references from a specific search site.
$searchengines: The total number of references from search engines.
$words{TO}{WORD}: The number of times a search for WORD resulted in a hit to a specific page.
$referer{TO}{FROM}: The number of times a specific page has been referenced from an off-site page.
$totalreferer: The number of non-image and non-CGI referenced from off-site

sub.morevars:

$countries{COUNTRY}: The number of hits from a specific country.
$ustypes{COM|EDU|ORG|MIL|NET}: The number of hits from a specific US domain type.
$months{##}: The number of hits during a given month.
$daysweektotal{##}: The number of hits on each of the days of the week.
$daysmonthtotal{##}: The number of hits on each of the days of the months.
$hits{DATESTRING}: The total number of page hits on a specific date.
$pagetotal{PAGE}: The total number of hits on a specific page.
$avgdates{##}: The average number of hits for each day of the months.
$avgdays{##}: The average number of hits for each day of the week.
$domaintotal{DOMAIN}: The total number of hits from a specific domain.
$weeks{####}: The total number of hits for a specific week.
$dirs{DIRECTORY}{total}: The total number of hits from files in a specific directory.
$dirs{DIRECTORY}{bytes}: The total number of bytes from files in a specific directory.
@pages: A list of all pages, sorted by most accesses to least.
@domains: A list of all domains, sorted by most accesses to least.
@countries: A list of all countries, sorted by most accesses to least.
@pagebytes: A list of all pages, sorted by most bytes transferred.
@dates: A list of all dates, sorted by most accesses to least.
@users: A list of all users, sorted by most access for current month.