In a nutshell: We can defrost frozen food by using a refrigerator, under running tap water, and a microwave oven. However, food should never be defrosted at room temperature or in hot water. Foods that are not defrosted in the refrigerator should be cooked and eaten immediately after defrosting. Always defrost frozen food to be consumed raw (or without further cooking) in a refrigerator. 

Remember: Food should never be defrosted at room temperature or in hot water, as this exposes food to temperature danger zone for extended periods of time, thus allowing bacteria to grow. Unless defrosted in the refrigerator, refrigerated food should be cooked immediately after defrosting, as higher temperatures encourage bacterial growth in food.

While both the microwave and running tap water are generally safe ways to defrost frozen food, they are more likely to expose frozen food to be consumed raw (or without further cooking) to the Temperature Danger Zone for some time or create hot spots* that promote bacterial growth. Therefore, using these methods for defrosting frozen food to be consumed raw (or without further cooking) is not recommended.
*hot spots: areas with uneven temperature distribution in food