A phoneme is the individual level of sound in speech. Throughout the mid-twentieth century, numerous theories have emerged in the attempt to precisely define the phoneme and provide an accurate model of its use across different languages. Linguistic schools in both the former Soviet Union and the United States developed a standard definition of the term around the 1950s: a phoneme is the smallest phonic (having to do with sound) constituent of a word form, one which cannot be broken down into smaller constituents. A phoneme is thus differentiated from something like a syllable, which can be broken down into constituent phonemes. For example, in the word “cantaloupe”, there are three distinguishable syllables (“can,” “ta,” and “loupe”), because syllables are broken down according to the presence of a vowel. However, each of these can further be broken down into the individuals sounds (phonemes) that make up the syllable (“can” = /c/, /a/, and /n/).

The definition of a phoneme is not the same as that of a letter, however, because there are several phonemes in different languages that are made up of multiple letters acting together. In English, a common, multi-letter phoneme is /th/, such as in the word “this.” The “th” in this word is the first distinguishable sound that the language produces. The theory of phonemes is even more important in a language like Russian, in which individual letters serve the same function as consonant clusters do in English. For example, the Russian letter “ч” (pronounced “ch”) takes the place of a sound that requires two letters in English. Thus, phonemes are distinguished entirely by their contributions to individual sounds in speech, not by how many letters make them up.

An allophone is a various articulation of the same phoneme. In general, each allophone can only occur in speech environments in which none of the other allophones of the same phoneme occur. Allophones are formed through the different enunciative positions the mouth can take. An example of this would be the English words “hot” and “top.” Here, both words consist of the /t/ phoneme. However, the word “top” enunciates the /t/ via complete aspiration of the letter, whereas the word “hot” enunciates the /t/ via a glottal stop (whereby a phoneme is pronounced and heard by the audible release of air from the airstream). Thus, phonemes in any language can have multiple different allophones.

In linguistics, a phoneme is the smallest unit of sound in speech. Reading instruction often includes teaching students to identify each phoneme in a word. For example, the word pan has three phonemes: /p/, /a/, /n/. 

An allophone defines the variations in phonemes. The word allophone is from the Greek words other and sound. Allophones describe phonemes whose sound changes depending on the letters that surround it. For example, the word kit has an aspirated sound to it (meaning that there is air being expelled rather forcefully when the "k" is pronounced). But in the word skit, the "k" sound is softened quite a bit by the "s" sound that precedes it. This is an allophone. 

There is an infinite number of allophones in the English language. This is because allophones are not only affected by the phonemes around them, but also by other factors like the communication situation, social class, and regional variations in dialect. 

A phoneme is the smallest unit of sound in speech. When children first begin to read, we teach that phonemes have distinctive sounds that are represented by letters and that each phoneme carries distinct word meaning. For example, the word 'cat' has three phonemes, 'c' 'a' and 't', but if 'c' is changed for the other phoneme 'mat', the meaning of the word changes.

Allophones are variations in the realization (or sound) of phonemes, like the different pronunciations of the phoneme 't' in the word 'tar' and the word 'letter', where the 't' allophone (sound) is softened to a 'd' sound. Allophones do not indicate a change in the meaning of the word, nor do they indicate a change in the phoneme used to make up the word.

A difference between the two is that changing the phoneme changes the meaning of the word, whereas changing the allophone changes the sound of the realization of word but does not change the meaning of the word. 

A phoneme is the smallest distinct unit of meaning in speech.  Phonemes go together to make up words.  For example, /p/ + /a/ + /n/ = pan.  Changing one of the phonemes will make the word have a different meaning.  For example, changing the /n/ to /t/ would make the word "pan" change into "pat", a word with a completely different meaning.  

Allophones are slight variations of the sound realizations of phonemes.  Allophones are often responsible for different manners of giving sound to speech.  For example, you could say the word "stop" with an explosive little puff of air at the end as the British do or you could say it by simply closing your lips on the p and not releasing any air as Americans do.  In either case, the phoneme has not changed - it is still a /p/, and the word meaning is still the same.  Each slight variations in sound realization in how the /p/ is expressed would be called an allophone.

A phoneme is a unit of sound in a language that cannot be analysed into smaller linear units and that can distinguish one word from another.

Phonemes are often presented surrounded by // in transcription (e.g. /p/ and /b/ in English pat, bat).

So /p/ and /b/ are two phonemes because they can distinguish between the words "pat" and "bat". /c/ is another, because it distinguishes the word "cat" from "pat" and "bat".

Allophones are any of the variants making up a single phoneme.

So, for example, you might pronounce the letter "T" differently in the two words "stand" and "tip". A common test to determine whether two phones are allophones or separate phonemes relies on finding minimal pairs: words that differ by only the phones in question. For example, the words tip and dip illustrate that [t] and [d] are separate phonemes, /t/ and /d/, in English.