To dropout: to fail to fulfill expectation, not complete a course (of study, generally). A person, varieties: college dropout or the much-maligned high school dropout.
Everyone's got their own reasons, and some of them are wonderful. Travel. Art. Family. Work. Enlightenment. Disillusionment.
Those of the high school variety may ameliorate the attendant social stigma by achieving their GED. Those opting for this route won't have to deal with another year of high school hell, and may well be lauded for their resourcefulness, especially if they're being otherwise productive with their time. Presented properly, and with self-confidence and rationality, a GED will get you most places a high school diploma will.
College dropouts, on the other hand, started into a project that's optional and costly. At some point, for some reason, we leave. While there is intention of return and closure, for our own sanity and to save face (for oneself or for the folks), we may say we're "taking time off" or "on leave". But as that time stretches, or as realization of the difficulty of returning sets in, or as self-esteem plummets, we may defeatedly defiantly claim "dropout". Plans change.