This is the 773rd most frequent Portuguese word.
seu
"Seu" means "your," "his," "her," or "their," depending on the context.
In this sentence, 'seu' functions as a possessive pronoun, indicating that the dog belongs to 'you'.
Este é seu cachorro.
This is your dog.
Here, 'seu' is again a possessive pronoun, referring to the behavior being attributed to 'you'.
Seu comportamento foi inadequado.
Your behavior was inappropriate.
In this case, 'seus' is the plural form of the possessive pronoun 'seu', referring to multiple pieces of advice belonging to 'you'.