The term 'vintage comics' refers to comic books from the Golden Age of Comics. The comics that were published during the 1940s and 1950s are extremely hard to find and it is rare to find these books in good condition. When you want to collect vintage comic books, you don't have to limit yourself to the 40s and 50s, though because the 1960s was also a good decade. During this period, there were hundreds of new comic books published, but they were done on a cheaper grade paper, so high grade comics from this period are rare as well.
During the 1970's, many people started to collect comics, so these books are not quite as valuable as ones from earlier times. What makes comics graded as vintage comics is the fact that they are hard to get, especially in mint or good condition. Since the 1970s the value of the vintage comic books has steadily increased because they are in high demand by collectors and investors alike.
If you are wondering what makes the comic books from earlier decades so valuable, you only have to look at the popularity of some of the superheroes that grew out of the pages of these comics. Superman, Spiderman, Batman, Flash Gordon and the Green Lantern are only a few of the popular names in comic book history. Archie, Popeye and Little Lule are also favorites, but the funny comics never quite gained the prominence of the superheroes.
Comic book art is a major factor in determining whether or not a comic book has any monetary value. If you have copies of artwork done by an artist that later went on to make a name for himself in the comic book world, you just may be in possession of a comic that could bring you in thousands of dollars.