LuckPerms

LuckPerms allows you to create groups for players and give them certain permissions.

Why is this useful compared to just using /op? Opped players have every permission, and you might not want to give all players full access to every command.

What can you do with LuckPerms?

LuckPerms allows you give certain groups of people specific permissions. For example, you could have a Moderator role who could switch gamemodes, teleport to other players and ban people, but would not have full OP.