Depends on how long you have before retirement, and what your savings goals are. The longer you have, and the higher your goals, the more riskier you will likely want to be. If one sector has a bad year or two, it won't hurt the overall performance of your portfolio. For those who are closer to retirement, or who are a little faint of heart at the idea of investing all their retirement savings into stocks, mutual funds are an excellent alternative or supplement. Mutual funds are 'baskets' of individual stocks.
Bonds are another option, and are almost risk-free.
But since stocks and mutual funds periodically dive in value, if you're 2 years away from retirement, you may not have the time to wait for their prices to rebound, and may prefer to have at least some of your savings invested in bonds. There are also, by the way, such things as 'bond funds' which operate on the same principal as mutual funds, but the individual shares are of government bonds. There are people out there who have made fortunes off of bond speculating, so there is money in bonds, particularly when the market is sluggish. Just leave it alone. If you've got more than a year or two to retirement, don't worry about it.