An open syllable is a syllable that ends in a vowel sound, such as the first syllable in "wiser." This is contrast to a closed syllable, which ends with a "coda" comprised of one or more consonants, as in the first syllable of "history."
The single-syllable words "blue," "tie" and "knee" are open syllables, while words such as "caught" or "slap" are closed syllables. Not all languages use both open and closed syllables. For example, the Hawaiian language allows only open syllables. Similarly, Japanese phonology allows only open syllables, with two exceptions. In certain cases, an "n" sound acts as a separate closed syllable; this is also true of doubled consonant sounds, such as in the English word "platter."