- Degree of substitution on nitrogen
Explanation:
Amines are derivatives of ammonia.
If one hydrogen of ammonia is replaced by an alkyl group, it is called a primary amine.
If two hydrogens of ammonia are replaced by alkyl groups, it is called a secondary amine.
If three hydrogens of ammonia are replaced by alkyl groups, it is called a tertiary amine.
So, tertiary, secondary, and primary amine represents the degree of substitution on the nitrogen.