<human>:  Explain the differences between a diphthong and a monophthong.
<bot>: A diphthong is a type of speech sound that comprises two adjacent vowel sounds, blending them together seamlessly within the same syllable. In comparison, a monophthong is a type of vowel sound that is produced by a single, constant tongue position without any noticeable change in the vowel quality, occurring within a single syllable. For example, the "ou" sound in the word "out" is a diphthong, while the "a" sound in the word "cat" is a monophthong.