Cash
Is the most familiar asset cash. It is used on portfolios as a defense against market downturns. If economic indicators are good and markets are performing well very little of your portfolio will be held in cash.
Bonds
Bonds are like loans, you lend your money and you get paid an interest rate while your money is on loan. The aim is to get your money back at the end of the term. The higher the risk of the bodies you lend your money to the higher the interest rate. i.e. US government bonds are deemed as very low risk and low return. A corporate bond (loan to a company) is deemed to be much higher risk therefore a higher interest rate is paid.
Equities
Also known as shares or stocks. (hence the terms stock market and stock exchange) Investing in shares is investing in a company. As a shareholder you benefit from the growth of the company. As a shareholder you can receive a dividends as an income and growth if the share price goes up as the company increases its profitability.
Property
Property is again a familiar asset class, our portfolios will have a small proportion of property in areas that individuals would unlikely have exposure to like office space, retail space etc.
Alternatives
These are typically funds that invest in a way that attempts to reduce risk and give good steady performance regardless of the market conditions.