Bachelor's degree
Until the 19th century, a bachelor's degree represented the first degree in a particular faculty, with Arts representing undergraduate study, thus the Bachelor of Civil Law (BCL) at Oxford and the Bachelor of Laws (LLB) at Cambridge, for example, were postgraduate degrees. Vestiges of this system still remain in the ancient universities, with Oxford and Cambridge awarding BAs for undergraduate degrees in both arts and sciences (although both award undergraduate BTh degrees through associated theological colleges, and Oxford awards BFA degrees in addition to the BA) and defining other bachelor's degrees (e.g. BPhil, BCL) as postgraduate awards equivalent to master's degrees, although many postgraduate bachelor's degrees have now been replaced by equivalent master's degrees (e.g. LLM for the LLB at Cambridge and MSc for the BSc at Oxford). The same historical usage of indicating an undergraduate degree by it being in the faculty of arts rather than being a bachelor's degree gives rise to the Oxbridge MA and the Scottish MA).
Bachelor of Arts and Science
Bachelor of Arts and Science (B.A.S. or B.A.&Sc. or B.A.Sc.) is an undergraduate bachelor's degree conferred by a small number of American universities and a fair number of universities in other English-speaking countries (including Canada and Australia). Generally, to receive a B.A.S. degree, a student would need to complete the general requirements for a bachelor's degree and also the requirements for two different academic majors (or academic minors) — one that usually leads to a B.A. degree and one that usually leads to a B.S. degree. In the United States, the degree is meant to be a four-year degree, but many students will take five years to complete the program.