Not defining "BERT" is a little weird, especially since something like MLM is explained. A good rule for writing, which I learned from The Economist, is to explain what something is the first time you mention it. It does lead to some funny explanations sometimes. One of my favorites, again from The Economist, is "HSBC, a bank". It sort of let them know that even if they see themselves as being big and important, they are "just a bank".