(Writing Systems: An introduction to their linguistic analysis, Florian Coulmas)
Intuitive notions of the syllable are vague. Attempts at precision move the discussion to a different level of analytical notions defined in a theoretically justified way. In phonology, the syllable is seen either as the minimum unit of sequential speech sounds or as a unit of the metrical system of a language. Certain theories consider the syllable as a basic phonological unit 'sui generis', while others derive its properties from those of the composite phonemes. Clearly, a syllable is a unit of articulation, and although a universally accepted articulatory definition is not available, phoneticians of different schools are agreed that syllables possess psychological reality for speakers. A syllable is a unit of speech that can be articulated in isolation and bear a single degree of stress, as in English, or a singles tone, as in Chinese. Different languages allow for different syllables. The specific structure of possible syllables is thus part of the phonological system of a language. In very general terms, syllables are units of speech consisting of an obligatory nucleus, usually a vowel (V), and optional initial and final margins, usually consonants (C). An alternative way of describing the structure of the syllable is to divide it into onset and rhyme, where the onset is the initial margin and the rhyme is further subdivided into peak and coda. A syllable with a vowel in coda position is called 'open', and a syllable with a consonant in coda position 'closed'.
The syllable is also the domain of stress, another feature of cross-linguistic variation. In French, stress is not very important, it rarely affect meaning. In English it can be distinctive, as in 'increase with stress on the first syllable, a noun, and in'crease, a verb, stressed on the second syllable. (...)
In some languages vowel length is distinctive, which means that there are minimal pair of syllables that differ in phonological time only. (...)
The syllable further function as the unit to which a pitch level is assigned. Languages that use pitch level to distinguish words are known as 'tone languages', and distinctive pitch levels are called 'tones'. In tone languages it is relations between the pitch of different syllables rather than the absolute pitch that is important. (...)
To summarize, segmental composition, stress, duration and tone are properties of the syllable. The importance of these features varies across languages and, although the syllable is crucial as a unit within which the distribution of phonological features can be stated, it is best defined as a unit for each language separately. This has important consequences for the analysis of syllabic writing systems.