The phancy name for this phonetic phoolishness is a diphthong, pronounced díf-thong, or also díp-thong.
To complete the discussion of Korean vowels, we must complete the discussion of diphthongs.
the discussion? I didn't know it had started!
Um, yes. You see, we've actually sneaked this concept in on you earlier. All those "y-vowels" are actually diphthongs (for example, blending the sound into gives us the sound).
We didn't tell you earlier because we didn't want your brain to explode from information overload.