* Monophthongs: These are single, pure vowel sounds, produced with a single, unchanging position of the tongue and mouth. Examples include the "a" in "cat," the "e" in "bed," and the "o" in "hot."
* Diphthongs: These are vowel sounds that glide from one vowel position to another within a single syllable. They start with one vowel sound and then move towards another. Examples include the "oy" in "boy," the "ow" in "cow," and the "ai" in "rain."
There are also other ways to categorize vowel sounds, such as by their height and frontness/backness in the mouth, but these are the two most fundamental types.