Log spam (or referral spam) is used by blackhatters to get backlinks to their pages from public logs of other – often unrelated – web sites.
A normal way to get your link on someone else's log would be to link to one of that other person's pages. Every time someone clicks on the link, the referring page is listed on the log.
Of course, blackhat optimisers prefer to fake the link, or at least make it invisible to the search engines' spiders. They use little scripts or pieces of automated software to fill people's logs with links.
Most webmasters hate their logs getting filled with junk links. I for one can't be bothered, so if you want to spam my log, be my guest. (See below for the links to my site stats).
[direct link] [direct link]
P.S.: The stats counters often don't show instant results. It typically takes about 30 minutes for your link to show on the lists — sometimes more, sometimes less. If you don't see it appear right away, come back a little later. You can use this button ( ) to drag to your bookmarks/favourites bar, for later reference…
Disclaimer: BlackHatKnight does not endorse email spam. That is illegal and it has nothing to do with log spamming.