The American Heritage Dictionary defines "degree" as being the actual title given to one who has completed a course of study. "Diploma" is defined as the document presented to the student upon completion.
Diplomas are often handed out for simpler courses of study, such as upon completion of high school. Those who finish a course of study at a college or university are said to have earned a degree. Diplomas in nursing and business schools also indicate shorter length of study and less specialization than degrees from a university in the same fields.
Diploma programs for business, for example, can be as short as under a year; diploma programs for nursing can take two to three years. Sometimes a diploma program can be a subset of a degree program. To continue the example, degree programs for both nursing and business usually require at least three to four years.
Diploma programs provide education within your given field and get you into the work force sooner. Degree programs give more in-depth knowledge and potentially let you start at a higher level.
Have a plan in mind before you decide on a program. Read all information carefully because different schools may define the terms slightly differently. Be aware of what your dream position actually requires in the way of education.