Managing an investment portfolio can be compared to tending a garden. In the beginning, you might plant as many roses as tulips. But after a few years, the roses have grown huge and threaten to choke the entire flowerbed. Rebalancing simply means cutting back the roses and planting more tulips to restore the balance.
In the financial world, order means maintaining the risk you originally decided on. If you decided to have 70 percent in stocks and 30 percent in bonds, but a massive bull market means your stocks suddenly make up 90 percent of your assets, you have taken on way too much risk. A stock market crash will now hurt you much more than you planned.