Ok
The absolute definition of offside: the attacker is beyond the defender by any margin (a toenail, etc). According to
@SuperiorXI, this should be changed to there being daylight between the attacker and the defender.
Relative: measurement and referee and angle error may influence how marginal offside decisions are determined. Because of the relative, no matter where we draw the line, there will always be argument. However the purpose of changing the definition of offside is not to eliminate argument.
Thought exercise. Let's say that we have a robot drone capable of always making the right decision on offside with zero measurement error (relative). We still have to tell the robot what offside actually means (absolute). And it will be a valid debate between "any margin between attacker and defender" and "daylight between attacker and defender".