What the difference between 'post-secondary' and 'post-baccalaureate'?
'post-secondary' : after High School.
Children have a primary education (at a primary school) between the ages of 5 and 11 or 12, then secondary education (at a secondary school) till 16-18 years, prior to a possible tertiary education at a college or university.
Post-secondary education might involve going to a university, or an apprenticeship, or a Finishing School in Switzerland!
and 'post-baccalaureate': the baccalaureate is the bachelor's degree, the first degree that is granted by a college or university. Hence, studying for a Master's Degree would be post-baccalaureate studies.