The difference between major and minor prophets is the difference in length of their books. The major prophets are much longer and fewer in number. Minor prophets are shorter in length and greater in number.
The "major" and "minor" labels do not really imply that one set of prophets are more important than the other. Length is the main determining factor when deciding whether a prophet is major or minor. Both labels are used strictly within the Old Testament.
There are five books from the major prophets. Combined, these books contain 167 chapters, with the longest composed of 66. Isaiah, the longest, along with Jeramiah, Lamentations, Daniel and Ezekiel, make up the major prophets.
There are 12 books labeled minor prophets, and combined they only contain 67 chapters. The shortest has only one chapter. These can often be read in a single short sitting. The minor prophets are Hosea, Joel, Obadiah, Jonah, Micah, Nahum, Habakkuk, Zephaniah, Haggai, Zechariah and Malachi.
These books are contained within all Christian Bibles that have the Old testament and always appear in the same order within these Bibles. In Jewish texts, however, the prophets are often arranged differently. These books are all considered important to the foundation of both religions.