A change in a vowel sound caused by partial assimilation especially to a vowel or semivowel occurring in the following syllable. 元音变化尤指因与下一音节的元音或半元音的部分相似而引起的元音变化
A semivowel, one having an audible sound by the addition of another Letter;e.g.S and R. 半元音是由另一个字母辅助才能够发出声音的字母，比如S或R；
Produce the semivowel “r”[r] as in ROUGH, produce it again slowly, you’ll discover that this sound is actually [aur], a vowel sound starts it. 如ROUGH中的[r]就是一个半元音。
Syllable is a nonsignificant composite sound, made up of a mute and a Letter having a sound (a vowel or semivowel);for GR, without an A, is just as much a Syllable as GRA, with an A. 音节是由一个哑音字母和一个发声字母（元音或者半元音）构成的无意义的复合声音，没有A时GR是一个音节，而有A时GRA也是一个音节。
Study on Semivowel in Mongolian by Experimental Phonetics 蒙古语半元音实验语音学研究
The research on the semivowel by dynamic palatogram in Mandarin Chinese 普通话半元音动态腭位研究
