It stands for Bachelor of Medicine and Bachelor of Surgery. Its the British equivalent of an MD. Anyway, as for as your question goes regarding internship, if you're a foreign or international medical graduate, before you can do any kind of postgraduate medical training in the States, you have to be ECFMG certified. That means you have to pass USMLE Step 1 and USMLE Step 2 CS which are knowledge-based exams, and Step 2 CS, which is an assessment of your clinical skills. I'm assuming that you've already finished med school in the UK.