I found the following description.
For Automotive applications the following applies:
Critical Characteristic is a product feature, dimension or note that reasonably anticipated variation could directly affect compliance with government regulations or safe operation of the equipment. Any of those characteristics that affect a failure mode with a severity of 9 or 10 must be reviewed to determine if they should become a critical characteristic.
Significant Characteristic is a feature, dimension, or note that reasonably anticipated variation could affect principal fit, function, durability, customer satisfaction, or manufacturability. Any of those characteristics that affect a failure mode with a severity of 5 to 8 and an occurrence of 4 or higher must be reviewed to determine if they should become a significant characteristic