An inflection is a change in the form of a word that creates a grammatical variation without changing the word's core meaning. When you add -s to “cat” to make “cats,” or -ed to “walk” to make “walked,” you're using inflection. The word stays fundamentally the same; it just works differently in the sentence.

English uses inflection less than many other languages, but it still matters. Verbs inflect to show tense: “jump,” “jumps,” “jumped,” “jumping.” Nouns inflect to show quantity: “book” versus “books.” Pronouns inflect dramatically: “I” becomes “me” or “my” depending on how it's used in a sentence.

Some languages use far more inflection than English. In Latin, a single noun might have twelve different inflected forms. In Russian, adjectives change their endings to match the nouns they describe. English lost most of these complicated inflections over centuries, which makes it easier to learn in some ways but requires more precise word order to convey meaning.

The word can also mean a change in pitch or tone of voice. When your voice rises at the end of a question, that's an inflection. A monotone speaker talks without much inflection, while an animated storyteller uses lots of vocal inflection to make the story exciting.