The word aeon ( /ˈiːɒn/), also spelled eon or æon, originally means "life", and/or "being", though it then tended to mean "age", "forever" or "for eternity". It is a Latin transliteration from the koine Greek word ὁ αἰών (ho aion), from the archaic αἰϝών (aiwon). In Homer it typically refers to life or lifespan. Its latest meaning is more or less similar to the Sanskrit word kalpa and Hebrew word olam. A cognate Latin word aevum or aeuum (cf. αἰϝών) for "age" is present in words such as longevity and mediæval.

Although the term aeon may be used in reference to a period of a billion years (especially in geology, cosmology or astronomy), its more common usage is for any long, indefinite, period. Aeon can also refer to the four aeons on the Geologic Time Scale that make up the Earth's history, the Hadean, Archean, Proterozoic, and the current aeon Phanerozoic.

Roger Penrose uses the word aeon to describe the period between successive and cyclic big bangs within the context of conformal cyclic cosmology. In this theory, the remote future of the previous aeons becomes the Big Bang of subsequent aeons.

John the Baptist (Hebrew: יוחנן המטביל, Yoḥanan ha-mmaṭbil, Arabic: يحيى بن زكريا‎ Yahya ibn Zakariya, Aramaic: ܝܘܚܢܢ Yoḥanan, Greek: Ὁ Ἅγιος/Τίμιος Ἐνδοξος Προφήτης, Πρόδρομος καὶ Βαπτιστής Ἰωάννης Ho Hágios/Tímios Endoxos, Profḗtēs, Pródromos, kaì Baptistḗs Ioánnes) (c. 6 BC – c. AD 30-36) was an itinerant preacher and a major religious figure mentioned in the Canonical gospels and the Qur'an. He is described in the Gospel of Luke as a relative of Jesus who led a movement of baptism at the Jordan River. Some scholars maintain that he was influenced by the Essenes, who were semi-ascetic, expected an apocalypse, and practiced rituals corresponding strongly with baptism, although there is no direct evidence to substantiate this. John is regarded as a prophet in Christianity, Islam, the Bahá'í Faith, and Mandaeism.

Most biblical scholars agree that John baptized Jesus at "Bethany beyond the Jordan," by wading into the water with Jesus from the eastern bank. John the Baptist is also mentioned by Jewish historian Josephus, in Aramaic Matthew, in Pseudo-Clementine, and in the Qur'an. Accounts of John in the New Testament appear compatible with the account in Josephus. There are no other historical accounts of John the Baptist from around the period of his lifetime.