Complex sentence: In phonetics and phonology, checked vowels are those that usually must be followed by a consonant in a stressed syllable, whereas free vowels are those that may stand in a stressed open syllable with no following consonant.
Split into simpler sentences: In phonetics and phonology, checked vowels are those that usually must be followed by a consonant in a stressed syllable. Free vowels are those that may stand in a stressed open syllable with no following consonant.