(Hudur) is the heart's presence with Allah when it is absent from everything else. The slave can never be present with Allah except through one of His Beautiful Names and in so doing a state of perfect spiritual courtesy is maintained.
('Abd). The slave (and worshipper) is the one who is in a state of total and utter submission to the Will of Allah. After having been annihilated in Allah where all duality vanished and distinctions were erased, he returns to creation with perfect courtesy and with the Truth of Certainty that 'the Lord is the Lord and the slave is the slave'. When 'abd is translated as 'servant' it carries the implication that the servant can leave the service of his Master, if he so desires. However, the 'slave' is in total bondage, being utterly dependent upon his Master. All buying and selling transactions have been terminated. The slave belongs to Allah, completely, perfectly and unconditionally.
(Adab) is spiritual courtesy and gracious behaviour of the Path and perfect refinement of words and deeds. Adab is giving each thing and each moment its proper due. The science of the higher teaching is based upon adab, which encompasses all of human life. It extends from right behaviour with regard to the Sacred Law (Shari'a), right behaviour with one's fellow travellers, proper conduct towards the teaching and one's teacher, and reaches to unceasing spiritual courtesy to Allah Himself. The proper courtesy towards the Law is to stay within its boundaries, the proper conduct with regards to good actions is to complete the action and disconnect from it. Adab with regard to the Real is knowing what belongs to oneself and what belongs to Allah.
Each moment and each situation has it's own adab. It has been said that the higher teaching is all adab and the greater your understanding and implementation of proper conduct is, the higher you are in the teaching.