This word, of very varied meaning, corresponds to the two Hebrew terms: dôr, tôledôth. As a rendering of the later, the Vulgate plural form, generationes, is treated in the article GENEALOGY. As a rendering of the former, the word generation is used in the following principal senses.

It designates a definite period of time, with a special reference to the average length of man's life. It is in this sense, for example, that, during the long-lived patriarchal age, a "generation" is rated as a period of 100 years (Genesis 15:16, compared with Genesis 15:13, and Exodus 12:40), and that, at a later date, it is represented as of only 30 to 40 years.
The word generation is used to mean an indefinite period of time: of time past, as in Deuteronomy 32:7, where we read: "Remember the days of old, think upon every generation", and in Isaiah 58:12, etc.; of time future, as in Psalm 44:18, etc.
In a concrete sense, generation designates the men who lived in the same period of time, who were contemporaries, as for instance in Genesis 6:9: "Noah was a just and perfect man in his generations"; see also: Numbers 32:13; Deuteronomy 1:35; Matthew 24:34; etc.
Independently of the idea of time, generation is employed to mean a race or class of men as characterized by the same recurring condition or quality. In this sense, the Bible speaks of a "just generation", literally "generation of the just" [Psalm 13:6; etc.], a "perverse generation", equivalent to: "generation of the wicked" [Deuteronomy 32:5; Mark 9:18; etc.].
Lastly, in Isaiah 38:12, the word generation is used to designate a dwelling place or habitation, probably from the circular for of the nomad tent. Whence it can be readily seen that, in its various principal acceptations, the word generation (usually in the Septuagint and in the Greek New Testament: genea) preserves something of the primitive meaning of "circuit", "period", conveyed by the Hebrew term dôr.

Sources

GESENIUS, Thesaurus (Leipzig, 1829); FURST, Hebrew and Chaldee Lexicon (Leipzig, 1867); BROWN, DRIVER AND BRIGGS, Hebrew and English Lexicon (New York, 1906).

Bibliography Information
Obstat, Nihil. Lafort, Remy, Censor. Entry for 'Generation'. The Catholic Encyclopedia. https://www.studylight.org/encyclopedias/eng/tce/g/generation.html. Robert Appleton Company. New York. 1914.

Bible Encyclopedias Generation

The Catholic Encyclopedia

Bible Encyclopedias
Generation