To quote the classic and famous Gardner’s Art Through the Ages,
“Except when referring to the modern academic discipline, people do not often juxtapose the words ‘art’ and ‘history.’ They tend to think of history as the record and interpretation of past human actions, particularly social and political actions. Most think of art, quite correctly, as part of the present – as something people can see and touch. Of course, people cannot see or touch history’s vanished human events, but a visible, tangible artwork is a kind of persisting event. One or more artists made it at a certain time and in a specific place, even if no one today just knows who, when, where, or why. … Art historians seek to achieve a full understanding not only of why these ‘persisting events’ of human history look the way they do, but also of why the artistic events happened at all.”
The concept of art history is expanded upon in an article on Caravaggista. A list of recommended reading for those interested in learning more about the fundamentals of art history can be found here. Eager readers may want search Google Books for ‘art history,’ or read previews of commonly used art history books here (art historical methods), here (Gardner’s Art Through the Ages), and here (a primary source, Vasari’s Lives of the Artists).
If you are taking your first art history course and aren’t sure what to expect, check out this article.