Aorist ( /ˈeɪ.ərɨst/; abbreviated AOR) is a philological term originally from Indo-European studies, referring to verb forms of various languages that are not necessarily related or similar in meaning. In Indo-European languages such as Greek, Sanskrit, Armenian and Macedonian, as well as languages influenced by the Indo-European tradition, such as Georgian, the term is usually used for forms that express perfective aspect and often refer to past events. "Aorist" comes from Ancient Greek aóristos "indefinite", because it was the unmarked (default) form of the verb, and thus did not have the implications of the imperfective aspect, which referred to an ongoing or repeated situation, or the perfect, which referred to a situation with a continuing relevance, but described an action "pure and simple".

Because the aorist was the unmarked aspect in Ancient Greek, the term is sometimes applied to unmarked verb forms in other languages, such as the habitual aspect in Turkish.

In Proto-Indo-European, the aorist appears to have originated as a series of verb forms expressing manner of action. Proto-Indo-European had a three-way aspectual opposition, traditionally called "present", "aorist", and "perfect", which are thought to have been, respectively, imperfective, perfective, and stative (resultant state) aspects. By the time of Classical Greek, this system was maintained largely in independent instances of the non-indicative moods and in the nonfinite forms. But, in the indicative, and in dependent clauses with the subjunctive and optative, the aspects took on temporal significance. In this manner, the aorist was often used as an unmarked past tense, and the perfect came to develop a resultative use, which is why the term perfect is used for this meaning in modern languages.