A syllabary is a set of written symbols that represent (or approximate) syllables, which make up words. A symbol in a syllabary typically represents an optional consonant sound followed by a vowel sound. In a true syllabary there is no systematic graphic similarity between phonetically related characters. That is, the characters for "ke", "ka", and "ko" have no similarity to indicate their common "k"-ness.
The Japanese language uses two syllabaries, namely hiragana and katakana. They are mainly used to write grammatical words as well as foreign words, e.g. hotel is ho-te-ru in Japanese. The form of this word in Japanese also in a way explains why a syllabary is very useful for Japanese. The English language, on the other hand, does not have this kind of syllable structure. It would be rather cumbersome to write the English word extra in CV syllables.
The Indian languages and the Ethiopic language have alphabets (called abugidas by some scholars) that look like syllabaries to western eyes, but are not. They both use separate consonant and vowel signs. Most often, the vowel sign is added to the consonant sign which may give the impression of a syllabic unit.
See also Writing Systems.