This is the 340th most frequent Icelandic word.
börnum
"Börnum" means "children" (dative plural) in English.
The word 'börnum' is the dative plural form of 'börn' (children) in Icelandic, used here to indicate the indirect object (to whom the gifts were given).
Ég gaf börnum gjafir.
I gave gifts to the children.
In this sentence, 'börnum' is in the dative plural case because the preposition 'um' governs a prepositional phrase requiring the dative case.
Við töluðum um börnum í dag.
We talked about the children today.
Here, 'börnum' is also in dative plural form as it is governed by the preposition 'við', which requires the dative case in this context.