Some examples:

• Rental properties
• Stocks (never buy stocks with money you can't miss for at least 5 or 10 years)
• Gold (it is often considered more an insurance against the failure of your other investments)

You might consider your own home an investment because you can sell it later when the kids have moved out and you need additional money to fund your retirement. But it doesn't generate any income as long as you're living in it and it does generate a lot of expenditure.

That's why it may be a smart move to buy a small house for yourself and invest as much money as possible in things that do generate income.