Question: I am a high school senior and am wondering if, in applying early decision, there are any terms that prohibit transferring to a different college for the second semester. If you apply early decision are you making a commiment to attend your university for four years or just for one semester?
There's no rule that we know of that prevents an early-decision applicant from transferring out after one semester, however doing so could be stressful and probably even costly (e.g, new application fees, possible moving expenses). It seems that, while no one can guarantee that a student/school match will bring true love, you should not apply ED without the conviction that the college in question is right for you. (Since you indicate that you're a senior, we wonder if you've already been admitted ED and are now questioning your choice. This happens sometimes, and, if so, you should focus on the pluses of this place that initially attracted you. Perhaps an overnight on campus will help get you psyched.)
Moreover, transferring as a second-semester freshman can be tricky. If space is available, you can usually get admitted to a college that is less selective than the one you're already in (or possibly on the same level). You won't, however, be able to "trade up" to an institution that wouldn't have admitted you straight from high school. In order to make that sort of move, you'll need to spend at least a year--and possibly two--proving yourself at your first college. In addition, if you're applying for financial aid, some colleges have little or no money for mid-year transfers. Always ask about that well in advance.
If, however, your ED uncertainty is linked to financial fears (i.e., your ED college didn't give you the kind of aid you feel you require), contact the financial aid folks there and share your concerns and also speak to your guidance counselor immediately about what other options may still be open to you.