Dutch orthography distinguishes between checked vowels and free vowels.

The free vowels are:

The terms checked vowel and free vowel originated in English phonetics and phonology.

In early Middle Dutch, short vowels were lengthened when they were free (in open syllables), so that any free vowel was now long by default.

Therefore, they are also known as checked vowels, whereas the tense vowels are called free vowels since they can occur in any kind of syllable.

A free vowel is not followed by a consonant in the same syllable (the syllable is open), a checked vowel is (the syllable is closed).

Therefore, these vowels are also called checked vowels, as opposed to the tense vowels that are called free vowels because they can occur even in open syllables.

The only exception is the Free Play wedge, on which the player may call a consonant for $500 per occurrence, call a free vowel, or solve the puzzle, with no penalty for a wrong letter or answer.

In phonetics and phonology, checked vowels are those that usually must be followed by a consonant in a stressed syllable, while free vowels are those that may stand in a stressed open syllable with no following consonant.

In Germanic languages, lax vowels generally occur only in closed syllables and so are also called checked vowels, whereas the tense vowels are called free vowels as they can occur even at the end of a syllable.