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[C + singular or plural verb] all the people of about the same age within a society or within a particular familyThe younger generation smoke/smokes less than their parents did.
There were at least three generations - grandparents, parents and children - at the wedding.
It's our duty to preserve the planet for future generations.
This painting has been in the family for generations.
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[C + singular or plural verb] a period of about 23 to 30 years, in which most human babies become adults and have their own childrenA generation ago, home computers were virtually unknown.
first/second/third, etc. generation describes the nationality of someone belonging to the first/second/third, etc. group of people of the same age in the family to have been born in that countryShe's a second generation American (= her parents were American, although their parents were not).