What is an allophone?

Definition
	An allophone is a phonetic variant of a phoneme in a particular language.

Examples (English)
	[p] and [pH] are allophones of the phoneme /p/. [t] and [tH] are allophones of the phoneme /t/.

Examples (Spanish)
	[b] and [B] are allophones of the phoneme /b/. [d] and [D] are allophones of the phoneme /d/.