What is the temperature where small bubbles first start to form in saturated liquid called?

The temperature at which small bubbles first start to form in a saturated liquid is referred to as the bubble point. This term is specifically used in thermodynamics and phase change phenomena to indicate the precise condition at which a liquid begins to transition into vapor form, though the liquid remains saturated. At the bubble point, the vapor pressure of the liquid equals the surrounding pressure, allowing the small vapor pockets to nucleate and form bubbles within the liquid.

In contrast, the boiling point is defined as the temperature at which a liquid turns to vapor at a specific pressure, often implying that the entire liquid is rapidly converting to gas. The melting point refers to the temperature at which a solid becomes a liquid, which is unrelated to the phase shift described in the question. Bubbling point, while it may seem relevant, is not a standard term used in thermodynamics; thus, it is not the correct choice. The terminology surrounding these concepts is crucial for understanding refrigeration cycles and phase behavior in HVAC systems.