Output Units of Soil Moisture Sensor
It's giving you units of "wetness", from 0 meaning "bone dry", and 950 meaning "sopping wet".

It's for an Arduino. It doesn't give you anything as technical as real units - just a rough scale between wet and dry. It's entirely up to you how you interpret that value.

It's about as accurate as sticking your finger in the soil to feel how wet it is.

You could divide the sampled value by 10 and use it as a percentage of sogginess.