The Hebrew word kodesh means "separateness," "exclusiveness."

"Holiness" of God is the Spiritual Essence of God, His expression of the highest, exclusive spiritual purity of the Truth of His Will, His Laws, Commandments, "set apart", separated from all other laws of man, from his religious false teachings and various fabrications. 

"Holiness" of Jesus Christ is the state of righteousness, purity, acquisition of the spiritual "Image" and "Likeness" of God achieved by His perfect knowledge and fulfillment of the Will of God, His Commandments.

"Holiness" of man is the spiritual and moral purity of man, living in separation from sin, achieved by knowledge, fulfillment of God's Will, separation from everything that contradicts it.  

 The words translated as "holy" (hagios) and "holiness" (hagiasmos), also "sanctification" (hagiootes; hagiosyne), mean the "separation" of man to serve God, His Will, His Commandments.  

Translated with DeepL.com (free version)