This is the 110th most frequent Hungarian word.
neki
"To him/her/it" or "for him/her/it".
In this sentence, 'neki' acts as an indirect object pronoun meaning 'to him/her/them' depending on the context.
Adtam neki egy ajándékot.
I gave them a gift.
Here, 'neki' also indicates the recipient of an action, translated as 'for him/her/them'.
Ez a könyv neki van fenntartva.
This book is reserved for them.
In this instance, 'neki' functions as a dative pronoun, showing to whom the speech is directed.