I know that I'm kinda asking for a lot here, but can any of you give me, a person with lesser experience in physics, a basic explaination of spin? I've found out that a particle's spin can be compared to a transistor, but that didn't really tell me what it actually is. What does it define? For instance, meters define length, square meters define area, etc. Can anyone put what spin defines into those terms? Also, as a bonus question, what does relativistic mean in layman's terms?