This is the 100th most frequent Icelandic word.
allir
"Allir" means "everyone" or "all" in English.
In this sentence, 'allir' is used as a pronoun meaning 'everyone', referring to all the people being discussed.
Allir eru glaðir í dag.
Everyone is happy today.
Here, 'allir' is used as a descriptor adjective for 'nemendur' (students), emphasizing that every single student completed their task.
Allir nemendur skiluðu verkefninu á réttum tíma.
All the students submitted the assignment on time.
In this case, 'alla' is the accusative plural form of 'allur', agreeing with 'hjálpina' (the help) to denote inclusion of all help received.