What does “wajib is like fard in respect of action” mean?

Prescribed Acts and Prohibitions: Fard, Wajib, Sunnah, Nafl, Haram, Makruh, Azimah and Rukhsah

• Wajib must be performed and may not simply be omitted
• Wajib has exactly the same conclusive doctrinal status as fard
• Wajib applies only when accompanying a nafl act
• Performing wajib is only an optional extra