This is the 676th most frequent Icelandic word.
föstudag
The Icelandic word "föstudag" means "Friday" in English.
The word 'föstudaginn' in this sentence refers to a direct mention of Friday as a specific day when an action will take place. Its suffix indicates the definite form.
Við förum í bíó á föstudaginn.
We are going to the cinema on Friday.
Here, 'föstudaga' is in plural form to generalize about all Fridays, commonly expressed when talking about routines or recurring events.
Ég elska föstudaga því þá hefst helgin.
I love Fridays because the weekend begins then.
In this context, 'föstudögum' is in the dative plural form, used to indicate an ongoing or habitual activity occurring on Fridays.