Complex sentence: A front vowel is any in a class of vowel sound used in some spoken languages, its defining characteristic being that the tongue is positioned as far in front as possible in the mouth without creating a constriction that would make it a consonant.
Split into simpler sentences: A front vowel is any in a class of vowel sound used in some spoken languages. The defining characteristic of a front vowel is that the tongue is positioned as far in front as possible in the mouth without creating a constriction that would make it a consonant.