This is the 550th most frequent Greek word.
όλοι
"Όλοι" means "everyone" or "all" in English.
In this sentence, 'Όλοι' means 'everyone', acting as the subject of the sentence indicating all members of the specified group.
Όλοι πήγαν στην παραλία σήμερα.
Everyone went to the beach today.
Here, 'όλους' is in the accusative case, meaning 'all (of you)', indicating the entire group of people being thanked.
Ευχαριστώ όλους σας για τη βοήθεια.
I thank all of you for the help.
Here, 'όλοι' means 'everyone', acting as the subject of a dependent clause describing a reaction.