What is a working principle of VAV,RAG and SAG in air conditioning?

VAV: Variable Air Volume

RAG: Return Air Grill

SAG: Supply Air Grill

Air conditioning (often referred to as A/C, AC, or aircon) is the process of altering the properties of air (primarily temperature andhumidity) to more comfortable conditions, typically with the aim of distributing the conditioned air to an occupied space to improve thermal comfort and indoor air quality