zero degrees (Celsius); freezing point
Primarily refers to 0°C, the temperature at which water freezes. Often used in weather contexts.
今朝の気温は零度だった。
The temperature this morning was zero degrees.
水は零度で凍る。
Water freezes at zero degrees.
Can be used for zero on any scale, but most commonly refers to temperature. For other scales, context makes the meaning clear.
この計器の針は零度を指している。
The needle of this gauge is pointing to zero.
零度 is the everyday term for zero degrees Celsius, whereas 零点 is a more technical way to refer to that same zero point on a scale.
absolute zero
Compound of 零 (rei, 'zero') and 度 (do, 'degree').