There are five basic types of intervals which are listed as follows:
Perfect intervals are 4ths, 5ths and octaves. If you widen any of these intervals by a semitone they become augmented, and if you narrow them by a semitone they become diminished. Major intervals become minor if narrowed by a semitone and minor intervals become major if widened by a semitone.
Examples of intervals which can be major or minor are 2nds, 3rds, 6ths and 7ths. A diminished interval can be created by narrowing a perfect or minor interval by a semitone. An augmented interval can be created by widening a perfect or major interval by a semitone.