Phonemes

"Definition
 
A phoneme is the smallest contrastive unit in the sound system of a language.

Discussion
 
Phonologists have differing views of the phoneme. Following are the two major views considered here:

 
In the American structuralist tradition, a phoneme is defined according to its allophones and environments.
In the generative tradition, a phoneme is defined as a set of distinctive features.

Comparison
 
Here is a chart that compares phones and phonemes:

A phone is …	A phoneme is …
One of many possible sounds in the languages of the world.	A contrastive unit in the sound system of a particular language.
The smallest identifiable unit found in a stream of speech.	A minimal unit that serves to distinguish between meanings of words.
Pronounced in a defined way.	Pronounced in one or more ways, depending on the number of allophones.
Represented between brackets by convention. Example: [b], [j], [o]	Represented between slashes by convention. Example: /b/, /j/, /o/

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@Lingulinks

More info..

1. English Phonemes, Spellings, Example Words, and Meaningful Names
2. Making Friends With Phonemes