Self-Directed IRA - SDIRA
  
Most IRA investments are pretty boring. An IRA (individual retirement account) allows people to save for retirement, with the U.S. government giving tax incentives to help them. Typically, money in an IRA gets put into relatively vanilla investment vehicles, such as mutual funds.
A self-directed IRA lets the person get...weird. It opens up more unusual investment options.
SDIRAs allow a broader range of possibilities, including some forms of alternative investing. Examples include real estate and investments in private companies (as opposed to the dull, everyday practice of purchasing stock in public companies).
The SDIRA could even include money in things like horses or art, or precious metals (for you gold bugs out there, expecting the end of civilization, but still gaming those tax breaks). The key is that you still get the beneficial tax treatment from an IRA, with the added breadth of investment options.