VET as an organization
The Finnish Board of Film Classification (in Finnish, "Valtion Elokuvatarkastamo" or just VET) is the body that reviews audiovisual content. It was founded in 1946, and operates in Helsinki under the supervision of the Ministry of Education. Currently it's run by Matti Paloheimo.
Since the new less strict law of 2001, their job is to review movies (both the theater releases and VHS/DVD releases, of course), and register classifications of things they don't review themselves (this includes video games, both for computers and consoles).
And how they rate: the law about AV classifications and age limits
The new law is interesting because it allows the "adult" (sex, violence and horror) material to be almost completely uncensored¹ and needs not to be reviewed by the Board, provided it is not sold to minors. The age limits are supposedly better enforced now on the sales side; as the result, pr0n movies are available just about everywhere.
Also of note is that computer and console games now have a mandatory rating - but fortunately, the Board won't review the games, they just write down whatever classification the importer/distributor/game company provides. This has its advantages (The importers may actually have some good clue of the content of the game), and its disadvantages (Lazy importers may not give realistic results²).
The actual ratings that appear in products are S, 7, 11, 15 and 18. Often people use the old "K-" prefix: "K-15" would be "Kielletty alle 15-vuotiailta" (not for people under 15). S is "Sallittu" (Allowed for all ages). The rating is put inside of a circle (if the thing was reviewed) or a square (if it was voluntarily rated).
(Most of the information here was taken from VET's web page at http://www.vet.fi/.)
(For what it's worth, according to Pelit, the first game to get K-18 classification in Finland was Severance: Blade of Darkness...)
¹ pedophilia and bestiality are obviously banned...
² Toptronics slapped Myth III K-11, along with "Medium difficulty" rating... I'll give both Toptronics and VET a medal if they pass the game on first try with medium difficulty setting without using them blood-spillin' dwarves. Definitely K-15 and "Hard" if I had been rating it. =)