This is the 77th most frequent Hebrew word.
השני
"השני" means "the second."
In this sentence, 'השני' is used as an ordinal number referring to the second item in a sequence.
הכלב הראשון שחור, והשני לבן.
The first dog is black, and the second is white.
Here, 'השני' specifies the ordinal position of an item ('book') within a series.
אני רוצה את הספר השני בסדרה.
I want the second book in the series.
In this case, 'השני' is used as an ordinal number to identify which among a group ('child') is being referred to.