This is a breakout board for Honeywell's HIH-4030 humidity sensor. The HIH-4030 measures relative humidity (%RH) and delivers it as an analog output voltage. You can connect the output of the sensor directly to an ADC on a microcontroller; and, thanks to the sensor's near linear voltage output, the data is very easy to process.
Voltage applied to the supply pins should be within 4-5.8VDC, and optimally at 5V. The sensor will typically only consume about 200μA.
This product comes as shown in the picture, with the HIH-4030 soldered onto the breakout board. The pins of the 3-pin header are spaced by 0.1".