The Thermometer app measures the ambient room temperature or outdoor temperature received by your local weather station *.
If it has real old thermometer look with analog and digital readout, Celsius and Fahrenheit scale and Indoor / Outdoor option.
It also has an animated weather background option that shows the current weather conditions outside.
NOTE: The thermometer can measure and display the ambient temperature your device is in, but very few devices have dedicated ambient temperature sensors, so the temperature measured and displayed on most devices is the temperature of the device's internal electronics or battery, and this means the actual ambient temperature is only if the device is in standby for a long time. Therefore, the only correct way to know the actual ambient temperature is to launch this app immediately after waking your device that has been idle for at least an hour.
This limitation is not the fault of the application, and using this method you can measure the actual ambient room temperature with some degree of accuracy.