This is the 33rd most frequent Finnish word.
kaksi
Two.
Here 'kaksi' means the number 'two', used to indicate the quantity of books.
Minulla on kaksi kirjaa.
I have two books.
Here 'kaksi' (as 'kahteen', its translative case form) is used to describe the number in relation to division into parts.
Jaoin kakun kahteen osaan.
I divided the cake into two parts.
Here 'kaksi' appears in the adverbial form 'kaksistaan', indicating a group of two individuals acting together.