It's hard to say exactly what I mean when I say "art film," but you could always check out Wikipedia for its take on the term. It could be independent ("indie") films, though I'm not always going to be sure whether a film qualifies for that label or not, and even if it does, there are surely plenty of indie films that I would not label as "art films." There could be some things in my quirky movies section that would qualify as indie, and possibly art. Certainly many period pieces would qualify. It's often a total toss-up whether I dub a movie "art" or just drama. Heck, even some of the things in my weird movies section could be called art films. In fact, just about any genre could potentially qualify as an "art film," really.
Anyway, in spite of my not being a student of cinema, or anything, I kind of feel like some movies are just... more artistic than others. I dunno, I guess there's a certain sensibility... maybe it's little more than a feeling, when I watch certain movies, that the general American viewing audience wouldn't like them. (To be sure, there are some art films even I wouldn't care for.) Such movies can sometimes be a bit boring, or hard to watch for any number of reasons, such as emotional and/or physical suffering endured by the characters, for example. But I do like to occasionally indulge in movies that require you to actually think (and feel), more than most of the average big-budget Hollywood movies do. (Not, of course, that Hollywood can't make big-budget movies that are more than just mindless entertainment.) Of course, it's also important to sometimes watch movies that have some kind of "message," social commentary, something that illuminates the human condition, or what have you. Anyway... I dunno what else to say, so... whatever.