Vocales
From Latin vocalis, from vox, vocis (voice)
Vocales (vowels) are a type of letter that represent sounds made by letting air flow out of the mouth without any kind of interruption.
Spanish has 5 vocales: A, E, I, O, U. Notice there is no "Y" as a vowel — unlike English, y in Spanish is usually a consonant (though it can act as a vowel when it is alone or at the end of a word, as in y "and" or buey "ox").
The vowels , , and are known as Vocales Fuertes or Abiertas ("strong" or "open" vowels). The vowels and are known as Vocales Débiles or Cerradas ("weak" or "closed" vowels). This distinction matters when words with two adjacent vowels are split into syllables.
Note
Practice saying the vowels out loud and notice that the air flows out without interruption. Spanish vowels have cleaner, shorter sounds than English vowels — a is always "ah", e is always "eh", i is always "ee", o is always "oh", u is always "oo".