Gen. 2:4, "These are the generations," means the "history." 5:1,
"The book of the generations," means a family register, or
history of Adam. 37:2, "The generations of Jacob" = the history
of Jacob and his descendants. 7:1, "In this generation" = in
this age. Ps. 49:19, "The generation of his fathers" = the
dwelling of his fathers, i.e., the grave. Ps. 73:15, "The
generation of thy children" = the contemporary race. Isa. 53:8,
"Who shall declare his generation?" = His manner of life who
shall declare? or rather = His race, posterity, shall be so
numerous that no one shall be able to declare it.

In Matt. 1:17, the word means a succession or series of
persons from the same stock. Matt. 3:7, "Generation of vipers" =
brood of vipers. 24:34, "This generation" = the persons then
living contemporary with Christ. 1 Pet. 2:9, "A chosen
generation" = a chosen people.

The Hebrews seem to have reckoned time by the generation. In
the time of Abraham a generation was an hundred years, thus:
Gen. 15:16, "In the fourth generation" = in four hundred years
(compare verse 13 and Ex. 12:40). In Deut. 1:35 and 2:14 a
generation is a period of thirty-eight years.