Phonemes can be conceived as being the
smallest sound units in the language. When a
person learns a new language much of aural
understanding stems from a development of
phonemic discrimination.
The four links below provide various views of
phonemes.
Making Friends with Phonemes
Wikipedia provides concise definitions of
phonemes.
Answers.com expands on the concepts developed
by the two links above.
Romanization gives us an overview of the development of alphabetized systems for reading Chinese.