Soil pH is the measure of acidity or alkalinity in soil. It is measuredd on a scale from 1 to 14, which indicates soil nutrient availability.
Neutral soil would be at 7 on the scale. Numbers from 1 up to 7 are considered to be in the acidic range, numbers from 7 up to 14 are considered to be alkaline.
Most plants prefer a neutral to slightly acidic (6.5) soil. There are some plants, however, that will require sweeter or more alkaline soil.