What is a Biology major

is it someone who knows everything about biology,,

or someone who knows everything about biology in a certain area such as marine life or the human body?

A biology major doesn't even come REMOTELY close to knowing everything about biology. Hell, nobody knows everything about biology. If anything, a biology major knows a little bit about a lot of different subtopics of biology, i.e. microbiology, biochemistry, genetics, etc, whereas a Ph.D. knows a lot about a one or a few different topics.

Biology is the study of life from the cellular structure of plants and animals to the environmental issues of a local or global nature. A biologist investigates how organisms are structured, how they evolve, how their life processes function and how they interact with the rest of the environment. Most biologists conduct research to answer the basic questions of how organisms are interrelated. The result of this research can include advances in medicine and public policy. This major prepares you for a multitude of employment possibilities including graduate schools and careers in biomedicine and research, allied health, private industry, and education. Many pre-medicine, pre-dentistry and pre-veterinary science majors enroll in biology as their undergraduate major.