The Nephilim were the offspring of the "sons of God" and the "daughters of men" before the Deluge, according to Genesis 6:1-4. They are biblical creatures that are believed to have been giants.
A similar or identical biblical Hebrew term, read as "Nephilim" by some scholars, or as the word "fallen" by others, appears in Ezekiel 32:27. The word is loosely translated as giants in some Bibles and left untranslated in others. The "sons of God" have been interpreted as fallen angels in some traditional Jewish explanations. According to Numbers 13:33, they later inhabited Canaan at the time of the Israelite conquest of Canaan.
One of the most popular theories about the Nephilim is that they are relatives of (or are) Giants, or possibly Bigfoot. Most of the contemporary English translations of Genesis 6:1-4 and Numbers 13:33 render the Heb. Nephilim as "giants". This tendency in turn stems from the fact that one of the earliest translation of the Hebrew Bible, the Septuagint, composed in III/II century BCE, renders the said word as gigantes. The choice made by the Greek translators has been later adopted into the Latin translation, the Vulgate, compiled in IV/V century CE, which uses the transcription of the Greek term rather than the literal translation of the Heb. nefilim. From there, the tradition of the giant progeny of the sons of God and the daughters of men spread to later medieval translations of the Bible.
Others believe that the Nephilim were born when angelic beings and humans had children. All early sources refer to the "sons of heaven" as angels. From the third century BCE onwards, references are found in the Enochic literature, the Dead Sea Scrolls (the Genesis Apocryphon, the Damascus Document, 4Q180), Jubilees, the Testament of Reuben, 2 Baruch, Josephus, and the book of Jude (compare with 2 Peter 2). For example: 1 Enoch 7:2 "And when the angels, (3) the sons of heaven, beheld them, they became enamoured of them, saying to each other, Come, let us select for ourselves wives from the progeny of men, and let us beget children." Some Christian apologists, such as Tertullian and especially Lactantius, shared this opinion. The earliest statement in a secondary commentary explicitly interpreting this to mean that angelic beings mated with humans can be traced to the rabbinical Targum Pseudo-Jonathan and it has since become especially commonplace in modern Christian commentaries. This line of interpretation finds additional support in the text of Genesis 6:4, which juxtaposes the sons of God (male gender, divine nature) with the daughters of men (female gender, human nature). From this parallelism it could be inferred that the sons of God are understood as some superhuman beings.
Some suggest that Giants and Nephilim are one and the same, which they likely are. Like Giants, Nephilim stories most likely originated from cases of gigantism and stories of Mammoths.