There are a number of different academic degrees related to the study of architecture, all of which incorporate between five and seven years of total study. For someone intending to become a registered architect, there are three accredited professional degrees--the Bachelor of Architecture (BArch), Master of Architecture (MArch), and Doctor of Architecture (DArch). These three degrees are evaluated by the exact same professional criteria, as determined by the National Architectural Accrediting Board (NAAB), and are functionally equivalent within the profession of architecture.
Bachelor of Architecture
The BArch degree is traditionally a five-year program of study, most often begun directly out of high school, with no prior post-secondary education. These BArch programs are decidedly different from a four-year Bachelor of Arts (BA) or Bachelor of Science (BS) with a major in architecture, neither of which are considered professional degrees. There are currently 70 BArch programs accredited by the NAAB.
Master of Architecture
There is a bewildering variety of types of MArch degrees. The most common is a three-year program of study, following completion of an unrelated undergraduate liberal arts degree, for a total of seven years of post-secondary education-thus called a "4+3" program. Upon prior completion of a liberal arts degree (BA or BS) with a major in architecture, the accredited MArch program can typically be reduced to two years of study, or six years total--called a "4+2" program. However, to further confuse these options, a handful of schools still require three years of professional graduate education following a related undergraduate degree in architecture. There is another, unaccredited MArch option for those students with a professional BArch who wish to pursue further study. These programs most often require just one year of study and are typically called MArch II programs as they designate a second, post-professional degree.
Recently, a number of schools have begun eliminating their BArch programs, replacing them with five-year MArch programs. In almost every case, these programs are effectively the same as the five-year BArch programs, but with the added benefit of a master's designation. These are also fully accredited professional degrees, though they sometimes do require a portfolio review or other separate admissions process after the second, third or fourth years. They are called alternately 4+1, 3+2 or even 2+3 MArch programs, depending on when the interim period of portfolio and other holistic academic review occurs.
Doctor of Architecture
The DArch, like the MArch, can be either a first-professional (accredited) or post-professional degree. At present, only one first-professional degree program exists, the Architectural Doctorate (ArchD) conferred by the University of Hawaii.
Pre- & Post-Professional Degrees
This is a traditional four-year undergraduate degree, designed to provide a strong foundation in the liberal arts along with a general appreciation of design and construction. These programs can be seen as preparatory, "pre-architecture" degrees, or as the basis for future work in the many fields related to design and construction. Experience with general communication skills, writing, foreign languages, laboratory sciences and other liberal arts requirements can prove extremely beneficial throughout a successful career in any profession. However, these programs are not accredited by the NAAB, and thus further study is required in most states to receive a formal license to practice architecture.
The DDesign, MED, MS, and MA in architecture are all fancy names for post-professional study in architecture. None of these degrees are accredited by the NAAB, largely because almost all require their students to have previously received an accredited BArch, MArch, or DArch degree.
ArchD: Architectural Doctorate
BA: Bachelor of Arts
BArch: Bachelor of Architecture
BED: Bachelor of Environmental Design
BAS: Bachelor of Architectural Studies
BS: Bachelor of Science
DArch: Doctor of Architecture
MArch: Master of Architecture
MS: Master of Science (in architecture)
MA: Master of Art (in architecture)
MED: Master of Environmental Design (in architecture)
PhD: Doctorate of Philosophy (in architecture)
If all this information has raised more questions than it has answered, you're probably on the right track. If you're just entering the profession and hoping to become a licensed architect in the U.S., you should start by exploring the three NAAB-accredited degree tracks, which will require at least five years of study. The various pros and cons of all the different paths are largely dependent upon your interests, abilities, and economics. Find a program that interests you, in a place you will enjoy being. Success in architecture is fortunately more about the skills and abilities you have than it is about the specific degree type. Best of luck.