(Anglo-Saxon: perfect, or whole)
In the Old Testament the Hebrew, kadosch (holy), signified separation from the profane, dedication to God's service, e.g., the Israelites as people of God (Leviticus 20); Aaron as priest (1 Par. 23).
Applied to God it sets forth His separation from, and opposition to all evil.
Outside of God only that is holy which has some relation to Him.
Holiness of creatures can be subjective, objective, or both.
Subjective holiness in rational creatures consists essentially in sanctifying grace (separation from sin, possession of virtue).
Objective holiness in any creature denotes its exclusive dedication to the service of God: priests by ordination, religious by vows, sacred vessels, vestments, etc., either by consecration or by blessing.
New Catholic Dictionary