An infinitive absolute is the less common of the two kinds of Hebrew infinitive. more or video
Infinitive absolutes will never have a prefix (an infinitive with a prefix is an infinitive construct). The infinitive absolute is usually used to intensify the meaning of a prefix form of the verb (KHW 40.2a).
(Gen. 2:17) כִּי בְּיוֹם אֲכָלְךָ מִמֶּנּוּ מוֹת תָּמוּת׃