Definition of both determiner from the Oxford Advanced Learner's Dictionary

, pronoun
Oxford3000

both

determiner
bəʊθ
 
; boʊθ
 
 
1 used with plural nouns to mean ‘the two’ or ‘the one as well as the other’Both women were French.Both the women were French.Both of the women were French.I talked to the women. Both of them were French/They were both French.I liked them both.We were both tired.Both of us were tired.We have both seen the movie.I have two sisters. Both of them live in London/They both live in London.Both (my) sisters live in London.2 both… and… not only… but also…Both his mother and his father will be there.For this job you will need a good knowledge of both Italian and Spanish.
Usage noteUsage note: similarlyMaking comparisonsThis chart provides a comparison of the ways that teenage boys and girls in the UK spend their free time.In many cases, the results for boys and girls are virtually the same/identical.In many cases, the results for boys are virtually the same as/identical to the results for girls.Both boys and girls spend the bulk of their free time with friends.Most of the boys do more than two hours of sport a week, as do many of the girls.Like many of the girls, most of the boys spend a large part of their free time using the Internet.The girls particularly enjoy using social networking websites.Similarly, nearly all the boys said they spent at least two to three hours a week on these sites. Language Banks at contrast, illustrate, proportion, surprising