Abjads, or consonant alphabets, have independent letters for consonants and may indicate vowels using some of the consonant letters and/or with diacritics. In Abjads such as Arabic and Hebrew full vowel indication (vocalisation) is only used in specific contexts, such as in religious books and children's books.
The image below shows the word 'language' in Arabic and Hebrew, both without vowel marks (unvocalised) and with vowel marks (vocalised).