A change in the pitch, tone, or loudness of the voice.
She couldn't understand her grandfather's words, but she knew from his inflection that he was asking a question.
Changing the pitch, tone, or loudness of our words are ways we communicate meaning in speech, though not on the printed page. A rising inflection on the last syllable of a sentence generally indicates a question and a falling inflection indicates a statement, for example. Another way of inflecting words is by adding endings. We add -s to make nouns plural and -ed to put verbs in the past tense, and these changes are also referred to as inflections.