what are postgraduate and undergraduate mean?

does someone knows what postgraduate and undergraduate means?
thank advance

Undergraduate - A college or university student who has not yet received a bachelor's or similar degree.

Postgraduate - Of, relating to, or pursuing advanced study after graduation from high school or college.

http://www.dictionary.com

One generally hears these words on the university or college level. Like the definition Chilli showed us, undergraduate refers to a student who is pursuing, but has not yet received his/her bachelor's degree.

Postgraduate usually refers to those students in graduate school pursuing their master's or PhD.

In the US, "postgraduate" is usually just referred to as "graduate."