Daily Objectives are a feature in Killing Floor 2 that were introduced alongside the Vault. You are given three random objectives each day, which are worth 50,000 Vosh each. This allows you to more quickly work towards earning Vault Crates for cosmetic loot.

Possible Objectives Include:

Daily weapon Deal a certain amount of damage with a specific Weapon (amount varies per Weapon)
Daily zed Kill a specific Zed a certain number of times (amount varies per Zed)
Daily zed Kill any Boss (Endless Mode doesn't seem to count for this one)
Daily perk Earn 1,500 XP as a specific Perk
Daily character Win a Survival Mode match as a specific Character (must be alive when Boss dies)
Daily map Win a Survival Mode match on a specific Map on a specific Difficulty (it's never Normal Difficulty)

Regardless of if you complete them or not there will be three new objectives for you the next day.

Daily Objectives mostly exist to get players to branch out and try new things, but as they only help you work towards Vault cosmetics, they are entirely optional.