From the wiki glossary:
flux: transfer collateral between users
slip: modify a user's collateral balance
ink: collateral balance
The glossary does not make a distinct definition to user's collateral (gem) as opposed to urn's collateral (ink).
Hence, it might be better understood if flux description will be "transfer gem between users", or alternatively "transfer collateral token between users".
And similarly for slip.
This will make it easier to understand that these operations do not change the sate of a CDP/urn.