rank-difference correlation vs rank-order correlation

rank-difference correlation and rank-order correlation both are nouns.

Word	Noun	Adjective	Verb	Adverb
rank-difference correlation	Yes	No	No	No
rank-order correlation	Yes	No	No	No

As nouns, rank-difference correlation and rank-order correlation are synonyms defined as:

rank-difference correlation and rank-order correlation: the most commonly used method of computing a correlation coefficient between the ranks of scores on two variables

Other synonyms of rank-difference correlation include rank-difference correlation coefficient, rank-order correlation coefficient.

rank-difference correlation (noun)	rank-order correlation (noun)
the most commonly used method of computing a correlation coefficient between the ranks of scores on two variables	the most commonly used method of computing a correlation coefficient between the ranks of scores on two variables