A bachelor's degree is the diploma you get when you graduate from college. You might earn a bachelor's degree in Spanish literature or biology, for example. Sorry to break it to you: you cannot earn a bachelor's degree in beer pong.
For many college students, a four year program of study ends when they're awarded a bachelor's degree. This degree may be a BA, or Bachelor of Arts, or a BS, Bachelor of Science, depending on what subject the student majored in. If you continue beyond a bachelor's degree, you may earn a master's or even a PhD. A bachelor's degree is also called a baccalaureate, "university degree of a bachelor," from the Medieval Latin baccalaureus, "student with the first degree."