I am going to guess that it is a calcified brain tumor and they have determined in the imaging that it is benign?
If you can, please get a copy of the MRI or CT on CD and the report for yourself so you have all the exact details. This will help you understand exactly what you are dealing with. It may be that they may leave it, or depending on location or size, it may have to be removed.
Without many details, it is hard to respond. I hope after you see your doctor you get more answers.
sounds like it may be a calcified meningioma? Calcified often implies it's been there for a long time. Calcified tumors also tend to grow much slower or not at all. Like rumpled said, get a copy of the MRI report. What lead them to discover it? Are you having symptoms?