nt.number theory - Similarly Ordered

A theorem of Erdos states:

"There exists an absolute constant c such that, if n>ck, and if a₁/b₁, a₂/b₂, ... are the Farey fractions of order n, then a_x/b_x and a_x+k/b_x+k are similarly ordered."

Can someone provide a definition of "similarly ordered" as used here?

Thanks for any insight.

Cheers, Scott

@ARTICLE{Erdos:1943,
author={Erd{"o}s, Paul},
title={A note on {F}arey series},
journal={Quart. J. Math., Oxford Ser.},
fjournal={The Quarterly Journal of Mathematics. Oxford. Second Series},
volume={14},
year={1943},
pages={82--85},
issn={0033-5606},
mrclass={40.0X},
mrnumber={MR0009999 (5,236b)},
mrreviewer={G. Szeg{"o}}