Traditionally, nouns are declined (the set of all forms a noun can take is its declension) and verbs are conjugated (the set of all forms a verb can take is its conjugation).
While the nuance isn't important most of the time, it can be in some languages where, eg, some verbal forms can be both conjugated *and* declined, that is, they take endings that belong to both verbs and nouns (like the participle of Latin, which has four different verbal forms (present active, future active, perfect passive and future passive) but in *addition* to those is also declined like an adjective, with gender, case and number marking).
"Inflection" refers indifferently to conjugation or declinaison.