He has already had an mri done this is when they told him he has brain cancer and it isterminal my questio is what is terminal?

Life is terminal: None of us get out alive. In this case the doctors must feel the cancer is not curable, and thus is highly likely to result in his demise. Focus on quality time, even if it may be limited.

Non-curable: There are certain malignant brain tumors that are known to be incurable and probably the most common is is the glioblastoma multiforme (gbm) which has a mean survival of 14 months with maximal surgery/radiation/chemotherapy. There are characteristic features on MRI scans that are suggestive of gbm. It seems that is what your physicians are telling you-that the radiologic diagnosis is bad.