1. Contrastive distribution (parallel distribution) is when two sounds occur in the same phonetic environment or a similar one and there is a change in meaning. We call these sounds phonemes. E.g. Link and pink.
2. Free variation is when two sounds occur in exactly the same phonetic environment as one another. It does not cause a change in meaning. We call these sounds free variants, and they occur on the basis of dialect, education, and prestige. E.g. ئال قال كال
3. Complementary distribution is when two sounds occur in two separate phonetic environments. The sounds are used by speakers interchangeably and inconsistently without causing a change in meaning. We call these sounds allophones.
E.g. Milk and Lake (dark /l/ and clear /l/).