In Genesis, Japheth is the son of Noah associated with the peoples called the Javanites.
Genesis 10:2 lists Javan among Japheth’s sons. Javan is traditionally connected with Ionia and the Greeks, and the table of nations uses family relationships to organize peoples known to the biblical author. The exact historical identification of every name is debated, but the genealogy itself clearly places Javan under Japheth.
This question is distinct from the better-known genealogy connecting Canaan with Ham. Canaan is listed among Ham’s descendants in Genesis 10:6, whereas Javan appears in Japheth’s line. The term “Javanites” is a conventional way of referring to the peoples descended from or associated with Javan.