As I sometimes say, if you were to throw a stone down on the city of Ottawa you would probably hit a public officer holder. But I'll pull out the definition.
The designated public office holder is a specific group that the government has identified. It includes ministers, ministers of state, and their staff; deputy heads and assistant deputy heads; and assistant deputy ministers and those of comparable rank, which I have defined in a bulletin. An additional 11 were designated through regulations, primarily to cover individuals in the forces and individuals who were order in council in the Privy Council Office.
Parliamentary secretaries are not designated as public office holders.