1) Knee travel: The total vertical rise and fall of the knee assembly.
2) Throat distance: The maximum possible distance between the center of the spindle and the nearest obstruction measured perpendicular to the axis of the spindle. On a vertical drill press, the "obstruction" would typically be the cylindrical column on which both the drill head and the table are mounted. On a machine like the Bridgeport Series I, it would be the main machine casting.
3) Table to spindle: With the knee cranked all the way up and the spindle fully retracted, the distance between spindle nose and table surface.
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I guess it makes sense now. I left out that they also spec'ed Quill (Z Axis)......................5" so 7 - 5 = 2; I guess that is the minimum distance from the table to the spindle. Presumably that is less than zero if you add in a tool and holder.