A bulge-bracket bank, or BB, is a large global institution offering investment banking alongside businesses such as sales and trading, research, and asset management. An elite boutique, or EB, is an advisory-focused firm known for competing on major transactions without operating all the businesses of a universal bank. A middle-market bank, or MM, typically advises smaller or midsize clients, although the category covers a wide range of firms and deal sizes.
These labels are useful, but they are not rigid quality rankings. A strong middle-market group may have deeper expertise in a particular industry than a larger bank, and interview difficulty can vary considerably by office and team. You should research the actual group rather than relying only on the bank’s category.