Parfocal" refers to objectives that can be changed with minimal or no refocusing.
Parfocalling compound microscope objectives is a procedure which allows you to adjust each objective lens so that it will remain in relative focus with the other objective lenses on the microscope when switching from one magnifcation to the next. If microscope objectives are not parfocalled it means that you would need to refocus the microscope each time the objective turret is changed to a different magnification.