rank-order correlation vs rank-difference correlation

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

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

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

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

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

rank-order correlation (noun)	rank-difference 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