Morphophonology refers to the relationship between morphology and phonology - how the sound patterns of words change when their form changes. Some synonyms for this term include phonological morphology, sound change across morphemes, and morphophonemics. Morphophonemics refers specifically to the study of how morphological structures interact with phonological features. Other synonyms include morphological phonology, morphological alternations in sound patterns, morphophonetic change, and alternation rules in phonology. While these terms may have slightly different nuances, they all refer to the same concept of how the sound of words changes when their form changes due to morphological rules.