Phonological processes are changes that sounds undergo when combined in words and phrases. The main processes are assimilation, coalescence, elision, haplology, and metathesis. Assimilation occurs when one sound influences another nearby sound, making them more similar. Coalescence replaces two sounds with one sound containing features of both. Elision omits sounds in fast speech. Haplology drops similar consecutive sequences of sounds. Metathesis changes the order of sounds.