This is the 476th most frequent Icelandic word.
flestir
"Flestir" means "most" in English.
The word 'flestir' is used here to describe 'most' members of a specific group (in the class).
Flestir í bekknum kunna að synda.
Most people in the class can swim.
In this sentence, 'flestir' refers to a general majority of the subject (my friends).
Flestir vinir mínir búa í Reykjavík.
Most of my friends live in Reykjavik.
The term 'flestir' is applied here to indicate the largest proportion within a numeric timeframe (days in May).