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Backlash is backlash, it is the difference between the target position and the actual position

When accompanied by axis reversals - yes, due to machine flexing - no.

If you need more clarity then you can qualify it as screw backlash, gear backlash, or some specific type of backlash

Ask 1,000 machinists to define backlash and they will all tell you it has something to do with movement of the: handle, servo, stepper, etc., that happens before the axis actually moves. They may say it 1,000 different ways, but that's what they will mean.

Here's the first few definitions I find on google, it matches the dictionary definition precisely, argue away...

They all talk about axis movement. That doesn't mean that your Z-column has flexibility, causing unwanted movement, it means you are trying to move an axis and there is some sort of lag between the attempt and the actual movement that is caused by slop, or play, in the motion system.