Axiology is both a philosophy and a science of value.
Value is how you make an assessment of what is good, invaluable, worth, helpful or moral and what is bad, unvalued unworthy, harmful, or immoral.
 
Axiology can be thought of being an alternate title: theory of value.
 
Axiology, (from Greek axios, “worthy”; logos, “science”), also called the philosophical study of goodness, or value, in the widest sense of these terms.
 
Its significance lies (1) in the considerable expansion that it has given to the meaning of the term value and (2) in the unification that it has provided for the study of a variety of questions—economic, moral, aesthetic, and even logical—that had often been considered in relative isolation.
 
The term “value” originally meant the worth of something, chiefly in the economic sense of exchange value, as in the work of the 18th-century political economist Adam Smith. A broad extension of the meaning of value to wider areas of philosophical interest occurred during the 19th century under the influence of a variety of thinkers and schools.
 
Because “fact” symbolizes objectivity and “value” suggests subjectivity, the relationship of value to a fact is of fundamental importance in developing any theory of the objectivity of value and of value judgments. Whereas such descriptive sciences as sociology, psychology, anthropology, etc. all attempt to give a factual description of what is actually valued, as well as causal explanations of similarities and differences between the valuations, it remains the philosopher’s task to ask about their objective validity.