A Bachelor of Science (Bc., B.S., BS, B.Sc. or BSc; less commonly, S.B., SB, or Sc.B. from the Latin Scientiæ Baccalaureus) is an undergraduate

Bachelor's degree

A bachelor's degree is usually an academic degree awarded for an undergraduate course or major that generally lasts for three or four years, but can range anywhere from two to six years depending on the region of the world...

 academic degree

Academic degree

An academic degree is a position and title within a college or university that is usually awarded in recognition of the recipient having either satisfactorily completed a prescribed course of study or having conducted a scholarly endeavour deemed worthy of his or her admission to the degree...

 awarded for completed courses that generally last three to five years (see below).
In Australia, the BSc is a 3 year degree, offered from 1st year on. A fourth (Honours) year or an MSc is then required to progress on to PhD.
Many universities in Europe are changing their systems into the BA/MA system, and in doing so also offering the full equivalent of a B.Sc.