A traditional individual retirement account (IRA) is a vehicle through which you can put money away for retirement. Those contributions are tax deductible (depending on your income), maxed out at $5,500 per year, and then taxed the money is withdrawn during retirement. A Roth IRA is similar, except the contributions are made post-tax, and the withdrawals are tax-free.
The money you contribute to a traditional IRA is typically invested in stocks, bonds, or mutual funds. The difference between a traditional IRA and a self-directed IRA is that you have more investment options with a self-directed IRA: there are a number of alternative investments you could choose to store your money, like real estate, private mortgages, precious metals, intellectual property, private company stock, private market securities, and others.
Bottom-line: if you are interested in the advantages of an IRA but want more flexibility with where your money is invested, a self-directed retirement account may be right for you.