Question: What is an allophone?
Answer: A subtle variant of a phoneme.
ThoughtCo also has a concise explanation here: https://www.thoughtco.com/allophone-word-sounds-1689078 Allophones are a kind of phoneme that changes its sound based on how a word is spelled. Think of the letter t and what kind of sound it makes in the word “tar” compared with “stuff.” It’s pronounced with a more forceful, clipped sound in the first example than it is in the second. Linguists use special punctuation to designate phonemes. The sound of an l , for instance, is written as “/l/.”
British Council explains why being aware of allophones is important when teaching English here.