Investment Bank (IB)
  
See: Investment Banker. See: Bulge Bracket. See: Full-Service Bank.
The bank where you have a bank account is a commercial bank. They give you a roll of quarters for $25. They can advise you on your mortgage. They can get you credit cards.
An investment bank is a completely different animal. Investment bankers are real estate brokers, for the most part, who sell used shares, used companies, and sometimes new shares and new companies. They advise on mergers and acquisition. They take a spread in trading derivatives through their various desks in their brokerage divisions. Many have a Merchant Bank division, which manages global currency needs in commerce.
IBs pay serious money for starter-kit careers; you'll work 90 hours a week, sleep at the office a night or two a week, and after 2-3 years, you'll be perceived as having survived financial bootcamp. No spreadsheet will ever derive fear from you again.