Spotting or Period?

What is considered spotting and what is considered your period? Is there such thing as spotting right before your period? If I have brown discharge coming out very very slowly does that mean I'm on my period? I have a book about periods but this isn't answered! I've had my period for years now and I still don't know! I always have brown discharge before my period and I usually mark that as the date my period starts but when I do that makes my periods really long. I also cramp when I have the brown stuff! Help!