The Gray (Gy) is the SI unit used to measure the absorbed dose of ionizing radiation. It quantifies the amount of energy deposited per unit mass of matter that is exposed to radiation. The unit is defined as joules per kilogram ($J/kg$), making it a fundamental metric in the fields of dosimetry and radiophysics. Measurement using the Gray scale is critical for assessing biological risk from radiation exposure, allowing scientific assessment of tissue damage potential across various energy levels of radiation.