This is the 106th most frequent Swedish word.
deras
"Their" (possessive pronoun).
'Deras' is a possessive pronoun used to indicate that the house belongs to them (third person plural possessive).
Deras hus är mycket stort.
Their house is very big.
'Deras' is used here as a possessive pronoun to describe who the gifts belong to.
Vi såg deras presenter på bordet.
We saw their gifts on the table.
'Deras' in this sentence specifies ownership of the dog referring to a group.