Orthogonality

On different axies.

Two concepts that are orthogonal can be used (or happen) with or without each other freely,
and do not affect each other.

For a geometric example, perpendicular lines are orthogonal.

For a general example, the metric system and the imperial system are orthogonal. While they
are not usually used together, there is nothing wrong with saying millipounds or kilofeet.
On the other hand, the imperial system and SI Units are not orthogonal. SI uses 'meters' where
the imperial system uses 'feet' (and 'inches' and 'miles').