The LDR gives out an analog voltage when connected to 3.3V, which varies in magnitude in proportion to the input light intensity on it.Basically, here the variation in light intensity is read as change in the voltage. That is, the greater the intensity of light,lesser is the resistance and hence the corresponding voltage drop across the LDR will be lower too( because V=I*R, hence change in resistance is reflected as change in voltage). Since the LDR gives out an analog voltage, it is connected to the analog input pin on the Bolt module which has a built-in ADC (analog-to-digital converter), that converts the analog voltage (from 0-3.3V) into a digital value in the range of (0-1023). When there is sufficient light in its environment or on its surface, the converted digital values read from the LDR through the Bolt module will be in the range of 800-1023. So the value 1.02 thousand(1023) which you obtained does not have any unit but is a mere mapping of the analog voltage to the integer value in the range of 0-1023 by the inbuilt ADC(Analog to digital converter) and the corresponding value is displayed on the screen.