What is the glossary definition of "visual size"

Here is the documentation from the Qt ScrollBar element:

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visualSize : real

This property holds the effective visual size of the scroll bar, which may be limited by the minimum size.

This property was introduced in QtQuick.Controls 2.4 (Qt 5.11).

See also size and minimumSize.

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To me this is an example of a definition of "x is x'
I still don't know what visual size is.
I looked at both referenced items and I still don't know how
they apply to a scrollbar.

This is frustrating

I should also mention termsa; implicit Size The word "implicit" probably has a
technical definition but I don't know it. where is the glossary definition?
There are so many of these uses of jargon that the documentation writers
use that go undefined

I will also add that your property definitions include the name and type,
But there is no indication of "constant" (I..e. read-only) or setable.