In the context of an RTD (Resistance Temperature Detector) element specification, "BST" typically stands for "Base Sensing Temperature." This term refers to the temperature at which the resistance of the RTD element is specified or calibrated.

RTDs are often calibrated at a specific temperature to ensure accurate temperature measurements across a range of temperatures. This calibration point is known as the base sensing temperature or reference temperature. The resistance of the RTD at this temperature is often used as a reference point for temperature measurement calculations.

For example, if an RTD is specified as "Pt100 BST 0°C," it means that the RTD's resistance is calibrated or specified at a base sensing temperature of 0°C, and its resistance at this temperature is 100 ohms. This information helps in accurately determining the temperature based on the RTD's resistance-temperature relationship.